From 0c3dfb4c252c7d11c6e882b1bd437ff3811aa80a Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Fri, 24 Mar 2023 13:08:31 -0700
Subject: [PATCH 01/25] try sending a message with multiple recipients to the
 fake server

---
 test/net/smtp/test_smtp.rb | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index b418b3f..50916d6 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -560,6 +560,14 @@ def test_start_instance_invalid_number_of_arguments
       assert_equal('wrong number of arguments (given 5, expected 0..4)', err.message)
     end
 
+    def test_rcpt_to
+      port = fake_server_start
+      smtp = Net::SMTP.new('localhost', port)
+      smtp.start do |conn|
+        conn.send_message "test", "me@example.org", ["you@example.net", "friend@example.net"]
+      end
+    end
+
     private
 
     def accept(servers)

From a33eefd96149b6fa2648905adf649520dfae128a Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Fri, 24 Mar 2023 13:10:18 -0700
Subject: [PATCH 02/25] make test pass

---
 test/net/smtp/test_smtp.rb | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index 50916d6..228ad1b 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -639,6 +639,23 @@ def fake_server_start(helo: 'localhost', user: nil, password: nil, tls: false, s
             else
               sock.puts "535 5.7.8 Error: authentication failed: authentication failure\r\n"
             end
+          when /\AMAIL FROM: *<.*>/
+            sock.puts "250 2.1.0 Okay\r\n"
+          when /\ARCPT TO: *<(.*)>/
+            if $1.start_with? "-"
+              sock.puts "501 5.1.3 Bad recipient address syntax\r\n"
+            elsif $1.start_with? "~"
+              sock.puts "400 4.0.0 Try again\r\n"
+            else
+              sock.puts "250 2.1.5 Okay\r\n"
+            end
+          when "DATA"
+            sock.puts "354 Continue (finish with dot)\r\n"
+            loop do
+              line = sock.gets
+              break if line == ".\r\n"
+            end
+            sock.puts "250 2.6.0 Okay\r\n"
           when "QUIT"
             sock.puts "221 2.0.0 Bye\r\n"
             sock.close

From f68ca25eae8b8bdfccef25d65cf00051e2205e90 Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Fri, 24 Mar 2023 13:17:10 -0700
Subject: [PATCH 03/25] make a meaningful assertion

---
 test/net/smtp/test_smtp.rb | 1 +
 1 file changed, 1 insertion(+)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index 228ad1b..9ade0fc 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -566,6 +566,7 @@ def test_rcpt_to
       smtp.start do |conn|
         conn.send_message "test", "me@example.org", ["you@example.net", "friend@example.net"]
       end
+      assert_equal %w[you@example.net friend@example.net], @recipients
     end
 
     private

From d4ab4f99f4c5ba0d60c797f5b658d916f030c9ec Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Fri, 24 Mar 2023 13:17:31 -0700
Subject: [PATCH 04/25] actually save recipient during RCPT stage

---
 test/net/smtp/test_smtp.rb | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index 9ade0fc..fdf3cc2 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -577,6 +577,7 @@ def accept(servers)
 
     def fake_server_start(helo: 'localhost', user: nil, password: nil, tls: false, starttls: false, authtype: 'PLAIN')
       @starttls_started = false
+      @recipients = []
       servers = Socket.tcp_server_sockets('localhost', 0)
       @server_threads << Thread.start do
         Thread.current.abort_on_exception = true
@@ -648,6 +649,7 @@ def fake_server_start(helo: 'localhost', user: nil, password: nil, tls: false, s
             elsif $1.start_with? "~"
               sock.puts "400 4.0.0 Try again\r\n"
             else
+              @recipients << $1
               sock.puts "250 2.1.5 Okay\r\n"
             end
           when "DATA"

From 04b96d3964b88ab35edbe642dc2efae81ee481e2 Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Fri, 24 Mar 2023 13:41:01 -0700
Subject: [PATCH 05/25] try sending a message to a rejected recipient

---
 test/net/smtp/test_smtp.rb | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index fdf3cc2..a5753cb 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -569,6 +569,14 @@ def test_rcpt_to
       assert_equal %w[you@example.net friend@example.net], @recipients
     end
 
+    def test_rcpt_to_bad_recipient
+      port = fake_server_start
+      smtp = Net::SMTP.new('localhost', port)
+      smtp.start do |conn|
+        conn.send_message "test", "me@example.org", ["-you@example.net", "friend@example.net"]
+      end
+    end
+
     private
 
     def accept(servers)

From 1a432dc7fa20f2e9726112a790c1247687741c84 Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Fri, 24 Mar 2023 13:42:28 -0700
Subject: [PATCH 06/25] expect a syntax error with a server claiming bad
 address syntax

---
 test/net/smtp/test_smtp.rb | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index a5753cb..10e2d54 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -573,7 +573,9 @@ def test_rcpt_to_bad_recipient
       port = fake_server_start
       smtp = Net::SMTP.new('localhost', port)
       smtp.start do |conn|
-        conn.send_message "test", "me@example.org", ["-you@example.net", "friend@example.net"]
+        assert_raise Net::SMTPSyntaxError do
+          conn.send_message "test", "me@example.org", ["you@example.net", "-friend@example.net"]
+        end
       end
     end
 

From d17497ad5a1fc4ab00105cfbddcee3fa03b47ba8 Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Fri, 24 Mar 2023 13:43:42 -0700
Subject: [PATCH 07/25] try sending a message to a server with a temporary
 error for a recipient

---
 test/net/smtp/test_smtp.rb | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index 10e2d54..4966f39 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -579,6 +579,14 @@ def test_rcpt_to_bad_recipient
       end
     end
 
+    def test_rcpt_to_temporary_failure_recipient
+      port = fake_server_start
+      smtp = Net::SMTP.new('localhost', port)
+      smtp.start do |conn|
+        conn.send_message "test", "me@example.org", ["~you@example.net", "friend@example.net"]
+      end
+    end
+
     private
 
     def accept(servers)

From e38b81cec79c52f4fe6a3ab6cbc82d017d870afe Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Fri, 24 Mar 2023 13:44:18 -0700
Subject: [PATCH 08/25] expect a SMTPServerBusy error when an RCPT TO command
 is rejected

---
 test/net/smtp/test_smtp.rb | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index 4966f39..b62e8d0 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -583,7 +583,9 @@ def test_rcpt_to_temporary_failure_recipient
       port = fake_server_start
       smtp = Net::SMTP.new('localhost', port)
       smtp.start do |conn|
-        conn.send_message "test", "me@example.org", ["~you@example.net", "friend@example.net"]
+        assert_raise Net::SMTPServerBusy do
+          conn.send_message "test", "me@example.org", ["~you@example.net", "friend@example.net"]
+        end
       end
     end
 

From 33ba7c2d1240106f4fc7584ddff27257ddb5fdac Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Mon, 27 Mar 2023 13:45:02 -0700
Subject: [PATCH 09/25] be more realistic about return code for temporary
 failure

---
 test/net/smtp/test_smtp.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index b62e8d0..cb5c3f6 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -667,7 +667,7 @@ def fake_server_start(helo: 'localhost', user: nil, password: nil, tls: false, s
             if $1.start_with? "-"
               sock.puts "501 5.1.3 Bad recipient address syntax\r\n"
             elsif $1.start_with? "~"
-              sock.puts "400 4.0.0 Try again\r\n"
+              sock.puts "450 4.2.1 Try again\r\n"
             else
               @recipients << $1
               sock.puts "250 2.1.5 Okay\r\n"

From 2c50b7e1adf2e00b7066a82917f43e79ae0e3cc5 Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Mon, 27 Mar 2023 13:49:29 -0700
Subject: [PATCH 10/25] Add comments pertaining to SMTP error classes

---
 lib/net/smtp.rb | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/net/smtp.rb b/lib/net/smtp.rb
index 5ac208a..6042599 100644
--- a/lib/net/smtp.rb
+++ b/lib/net/smtp.rb
@@ -42,7 +42,7 @@ def initialize(response, message: nil)
         @message = message
       else
         @response = nil
-        @message = message || response 
+        @message = message || response
       end
     end
 
@@ -51,7 +51,7 @@ def message
     end
   end
 
-  # Represents an SMTP authentication error.
+  # Represents an SMTP authentication error (error code 53x).
   class SMTPAuthenticationError < ProtoAuthError
     include SMTPError
   end
@@ -66,7 +66,7 @@ class SMTPSyntaxError < ProtoSyntaxError
     include SMTPError
   end
 
-  # Represents a fatal SMTP error (error code 5xx, except for 500)
+  # Represents a fatal SMTP error (error code 5xx, except for 500 and 53x)
   class SMTPFatalError < ProtoFatalError
     include SMTPError
   end

From f8e4b642b98dc0586102c9ff3160df0fc1dd5f62 Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Mon, 27 Mar 2023 13:49:58 -0700
Subject: [PATCH 11/25] test for Net::SMTPMailboxPermanentlyUnavailable

---
 test/net/smtp/test_smtp.rb | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index cb5c3f6..8b909ed 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -589,6 +589,17 @@ def test_rcpt_to_temporary_failure_recipient
       end
     end
 
+    def test_rcpt_to_nonexistent_recipient
+      port = fake_server_start
+      smtp = Net::SMTP.new('localhost', port)
+      smtp.start do |conn|
+        assert_raise Net::SMTPMailboxPermanentlyUnavailable do
+          conn.send_message "test", "me@example.org", ["nonexistent@example.net", "friend@example.net"]
+        end
+      end
+      assert_empty @recipients
+    end
+
     private
 
     def accept(servers)
@@ -668,6 +679,8 @@ def fake_server_start(helo: 'localhost', user: nil, password: nil, tls: false, s
               sock.puts "501 5.1.3 Bad recipient address syntax\r\n"
             elsif $1.start_with? "~"
               sock.puts "450 4.2.1 Try again\r\n"
+            elsif $1.start_with? "nonexistent"
+              sock.puts "550 5.1.1 User unknown\r\n"
             else
               @recipients << $1
               sock.puts "250 2.1.5 Okay\r\n"

From 30b37978b44f32478238352940aca027069cc017 Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Mon, 27 Mar 2023 13:56:58 -0700
Subject: [PATCH 12/25] Add documentation for
 Net::SMTPMailboxPermanentlyUnavailable

---
 lib/net/smtp.rb | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/lib/net/smtp.rb b/lib/net/smtp.rb
index 6042599..38e202d 100644
--- a/lib/net/smtp.rb
+++ b/lib/net/smtp.rb
@@ -66,11 +66,16 @@ class SMTPSyntaxError < ProtoSyntaxError
     include SMTPError
   end
 
-  # Represents a fatal SMTP error (error code 5xx, except for 500 and 53x)
+  # Represents a fatal SMTP error (error code 5xx, except for 500, 53x, and 55x)
   class SMTPFatalError < ProtoFatalError
     include SMTPError
   end
 
+  # Represents a fatal SMTP error pertaining to the mailbox (error code 55x)
+  class SMTPMailboxPermanentlyUnavailable < ProtoFatalError
+    include SMTPError
+  end
+
   # Unexpected reply code returned from server.
   class SMTPUnknownError < ProtoUnknownError
     include SMTPError
@@ -510,6 +515,7 @@ def debug_output=(arg)
     # * Net::SMTPServerBusy
     # * Net::SMTPSyntaxError
     # * Net::SMTPFatalError
+    # * Net::SMTPMailboxPermanentlyUnavailable
     # * Net::SMTPUnknownError
     # * Net::OpenTimeout
     # * Net::ReadTimeout
@@ -583,6 +589,7 @@ def started?
     # * Net::SMTPServerBusy
     # * Net::SMTPSyntaxError
     # * Net::SMTPFatalError
+    # * Net::SMTPMailboxPermanentlyUnavailable
     # * Net::SMTPUnknownError
     # * Net::OpenTimeout
     # * Net::ReadTimeout
@@ -752,9 +759,11 @@ def do_finish
     #
     # This method may raise:
     #
+    # * Net::SMTPAuthenticationError
     # * Net::SMTPServerBusy
     # * Net::SMTPSyntaxError
     # * Net::SMTPFatalError
+    # * Net::SMTPMailboxPermanentlyUnavailable
     # * Net::SMTPUnknownError
     # * Net::ReadTimeout
     # * IOError
@@ -808,6 +817,7 @@ def send_message(msgstr, from_addr, *to_addrs)
     # * Net::SMTPServerBusy
     # * Net::SMTPSyntaxError
     # * Net::SMTPFatalError
+    # * Net::SMTPMailboxPermanentlyUnavailable
     # * Net::SMTPUnknownError
     # * Net::ReadTimeout
     # * IOError
@@ -1165,6 +1175,7 @@ def exception_class
         when /\A4/  then SMTPServerBusy
         when /\A50/ then SMTPSyntaxError
         when /\A53/ then SMTPAuthenticationError
+        when /\A55/ then SMTPMailboxPermanentlyUnavailable
         when /\A5/  then SMTPFatalError
         else             SMTPUnknownError
         end

From 8f5934d6da8cc96e2661ad30a24136dce01015a0 Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Mon, 27 Mar 2023 14:07:55 -0700
Subject: [PATCH 13/25] make sure it's the RCPT TO that fails

---
 test/net/smtp/test_smtp.rb | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index 8b909ed..898aaef 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -589,7 +589,7 @@ def test_rcpt_to_temporary_failure_recipient
       end
     end
 
-    def test_rcpt_to_nonexistent_recipient
+    def test_rcpt_to_nonexistent_recipient_send_message
       port = fake_server_start
       smtp = Net::SMTP.new('localhost', port)
       smtp.start do |conn|
@@ -600,6 +600,16 @@ def test_rcpt_to_nonexistent_recipient
       assert_empty @recipients
     end
 
+    def test_rcpt_to_nonexistent_recipient_rcptto
+      port = fake_server_start
+      smtp = Net::SMTP.new('localhost', port)
+      smtp.start do |conn|
+        conn.mailfrom "me@example.org"
+        conn.rcptto_list ["friend@example.net", "nonexistent@example.net"]
+      end
+      assert_empty @recipients
+    end
+
     private
 
     def accept(servers)

From d3beb536cc046c006d747ac97a885af3452d6c3e Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Mon, 27 Mar 2023 14:08:54 -0700
Subject: [PATCH 14/25] make test pass

---
 test/net/smtp/test_smtp.rb | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index 898aaef..e231128 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -605,9 +605,11 @@ def test_rcpt_to_nonexistent_recipient_rcptto
       smtp = Net::SMTP.new('localhost', port)
       smtp.start do |conn|
         conn.mailfrom "me@example.org"
-        conn.rcptto_list ["friend@example.net", "nonexistent@example.net"]
+        assert_raise Net::SMTPMailboxPermanentlyUnavailable do
+          conn.rcptto_list ["friend@example.net", "nonexistent@example.net"]
+        end
       end
-      assert_empty @recipients
+      assert_equal ["friend@example.net"], @recipients
     end
 
     private

From e9733341df5045e50c4524e9e4728bb1adedc178 Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Mon, 27 Mar 2023 14:41:41 -0700
Subject: [PATCH 15/25] add more rcptto_list tests

---
 test/net/smtp/test_smtp.rb | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index e231128..c83c493 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -612,6 +612,26 @@ def test_rcpt_to_nonexistent_recipient_rcptto
       assert_equal ["friend@example.net"], @recipients
     end
 
+    def test_rcptto_list_empty_list
+      port = fake_server_start
+      smtp = Net::SMTP.new('localhost', port)
+      smtp.start do |conn|
+        conn.mailfrom "me@example.org"
+        conn.rcptto_list []
+      end
+      assert_equal [], @recipients
+    end
+
+    def test_rcptto_list_all_nonexistent_recipients
+      port = fake_server_start
+      smtp = Net::SMTP.new('localhost', port)
+      smtp.start do |conn|
+        conn.mailfrom "me@example.org"
+        conn.rcptto_list ["nonexistent1@example.net", "nonexistent2@example.net"]
+      end
+      assert_equal [], @recipients
+    end
+
     private
 
     def accept(servers)

From 9871cafee2f1b9174c3a464e725a5011d089fee5 Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Mon, 27 Mar 2023 15:14:46 -0700
Subject: [PATCH 16/25] rcppto_list takes a block upon success, actually

---
 test/net/smtp/test_smtp.rb | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index c83c493..788b235 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -606,7 +606,7 @@ def test_rcpt_to_nonexistent_recipient_rcptto
       smtp.start do |conn|
         conn.mailfrom "me@example.org"
         assert_raise Net::SMTPMailboxPermanentlyUnavailable do
-          conn.rcptto_list ["friend@example.net", "nonexistent@example.net"]
+          conn.rcptto_list ["friend@example.net", "nonexistent@example.net"] do end
         end
       end
       assert_equal ["friend@example.net"], @recipients
@@ -617,7 +617,7 @@ def test_rcptto_list_empty_list
       smtp = Net::SMTP.new('localhost', port)
       smtp.start do |conn|
         conn.mailfrom "me@example.org"
-        conn.rcptto_list []
+        conn.rcptto_list [] do end
       end
       assert_equal [], @recipients
     end
@@ -627,7 +627,7 @@ def test_rcptto_list_all_nonexistent_recipients
       smtp = Net::SMTP.new('localhost', port)
       smtp.start do |conn|
         conn.mailfrom "me@example.org"
-        conn.rcptto_list ["nonexistent1@example.net", "nonexistent2@example.net"]
+        conn.rcptto_list ["nonexistent1@example.net", "nonexistent2@example.net"] do end
       end
       assert_equal [], @recipients
     end

From 788b88de36e7190d86f8c7065a0606818f82cdb1 Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Mon, 27 Mar 2023 15:21:28 -0700
Subject: [PATCH 17/25] these are both ArgumentError cases

---
 test/net/smtp/test_smtp.rb | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index 788b235..5eea5f3 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -617,7 +617,9 @@ def test_rcptto_list_empty_list
       smtp = Net::SMTP.new('localhost', port)
       smtp.start do |conn|
         conn.mailfrom "me@example.org"
-        conn.rcptto_list [] do end
+        assert_raise ArgumentError do
+          conn.rcptto_list [] do end
+        end
       end
       assert_equal [], @recipients
     end
@@ -627,7 +629,9 @@ def test_rcptto_list_all_nonexistent_recipients
       smtp = Net::SMTP.new('localhost', port)
       smtp.start do |conn|
         conn.mailfrom "me@example.org"
-        conn.rcptto_list ["nonexistent1@example.net", "nonexistent2@example.net"] do end
+        assert_raise ArgumentError do
+          conn.rcptto_list ["nonexistent1@example.net", "nonexistent2@example.net"] do end
+        end
       end
       assert_equal [], @recipients
     end

From 9f46846e1bf2c027d639112897501fcabbdd667e Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Tue, 28 Mar 2023 09:11:19 -0700
Subject: [PATCH 18/25] make tests pass

---
 lib/net/smtp.rb            | 17 ++++++++++++-----
 test/net/smtp/test_smtp.rb |  8 ++++----
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/lib/net/smtp.rb b/lib/net/smtp.rb
index 38e202d..3d0e37c 100644
--- a/lib/net/smtp.rb
+++ b/lib/net/smtp.rb
@@ -955,20 +955,27 @@ def mailfrom(from_addr)
     def rcptto_list(to_addrs)
       raise ArgumentError, 'mail destination not given' if to_addrs.empty?
       ok_users = []
-      unknown_users = []
+      unauthenticated_users = []
+      permanent_error_users = []
       to_addrs.flatten.each do |addr|
         begin
           rcptto addr
         rescue SMTPAuthenticationError
-          unknown_users << addr.to_s.dump
+          unauthenticated_users << addr.to_s.dump
+        rescue SMTPMailboxPermanentlyUnavailable
+          permanent_error_users << addr.to_s.dump
         else
           ok_users << addr
         end
       end
-      raise ArgumentError, 'mail destination not given' if ok_users.empty?
+      raise ArgumentError, 'all recipients rejected by server' if ok_users.empty?
       ret = yield
-      unless unknown_users.empty?
-        raise SMTPAuthenticationError, "failed to deliver for #{unknown_users.join(', ')}"
+      unless unauthenticated_users.empty?
+        raise SMTPAuthenticationError, "failed to authenticate for #{unauthenticated_users.join(', ')}"
+      end
+      # in this case there are mixed permanently-unavailable and OK recipients
+      unless permanent_error_users.empty?
+        raise SMTPMailboxPermanentlyUnavailable, "Recipient addresses failed: #{permanent_error_users.join(', ')}"
       end
       ret
     end
diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index 5eea5f3..aab30c1 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -589,7 +589,7 @@ def test_rcpt_to_temporary_failure_recipient
       end
     end
 
-    def test_rcpt_to_nonexistent_recipient_send_message
+    def test_rcpt_to_one_nonexistent_recipient_send_message
       port = fake_server_start
       smtp = Net::SMTP.new('localhost', port)
       smtp.start do |conn|
@@ -597,7 +597,7 @@ def test_rcpt_to_nonexistent_recipient_send_message
           conn.send_message "test", "me@example.org", ["nonexistent@example.net", "friend@example.net"]
         end
       end
-      assert_empty @recipients
+      assert_equal ['friend@example.net'], @recipients
     end
 
     def test_rcpt_to_nonexistent_recipient_rcptto
@@ -621,7 +621,7 @@ def test_rcptto_list_empty_list
           conn.rcptto_list [] do end
         end
       end
-      assert_equal [], @recipients
+      assert_empty @recipients
     end
 
     def test_rcptto_list_all_nonexistent_recipients
@@ -633,7 +633,7 @@ def test_rcptto_list_all_nonexistent_recipients
           conn.rcptto_list ["nonexistent1@example.net", "nonexistent2@example.net"] do end
         end
       end
-      assert_equal [], @recipients
+      assert_empty @recipients
     end
 
     private

From f82ba436eb8be0e1035f884990b310fe888807be Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Tue, 28 Mar 2023 09:15:10 -0700
Subject: [PATCH 19/25] test for mixed recipient status

---
 test/net/smtp/test_smtp.rb | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index aab30c1..53459c5 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -636,6 +636,18 @@ def test_rcptto_list_all_nonexistent_recipients
       assert_empty @recipients
     end
 
+    def test_rcptto_list_some_nonexistent_recipients
+      port = fake_server_start
+      smtp = Net::SMTP.new('localhost', port)
+      smtp.start do |conn|
+        conn.mailfrom "me@example.org"
+        assert_raise Net::SMTPMixedRecipientStatus do
+          conn.rcptto_list ["friend@example.net", "nonexistent1@example.net", "nonexistent2@example.net", "friend@example.com"] do end
+        end
+      end
+      assert_equal ["friend@example.net", "friend@example.com"], @recipients
+    end
+
     private
 
     def accept(servers)

From ee5d0ad0bb7a47d2f0c9851c896dc45b700a2144 Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Tue, 28 Mar 2023 10:25:28 -0700
Subject: [PATCH 20/25] test to ensure one string and one-element list are the
 same

---
 test/net/smtp/test_smtp.rb | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index 53459c5..c2f2db2 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -560,7 +560,25 @@ def test_start_instance_invalid_number_of_arguments
       assert_equal('wrong number of arguments (given 5, expected 0..4)', err.message)
     end
 
-    def test_rcpt_to
+    def test_send_message_rcpt_to_string
+      port = fake_server_start
+      smtp = Net::SMTP.new('localhost', port)
+      smtp.start do |conn|
+        conn.send_message "test", "me@example.org", "you@example.net"
+      end
+      assert_equal %w[you@example.net], @recipients
+    end
+
+    def test_send_message_rcpt_to_single_list
+      port = fake_server_start
+      smtp = Net::SMTP.new('localhost', port)
+      smtp.start do |conn|
+        conn.send_message "test", "me@example.org", ["you@example.net"]
+      end
+      assert_equal %w[you@example.net], @recipients
+    end
+
+    def test_send_message_rcpt_to_two_of_them
       port = fake_server_start
       smtp = Net::SMTP.new('localhost', port)
       smtp.start do |conn|

From ceccdaf7053db7bac127bb30316ce0ad273d5226 Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Tue, 28 Mar 2023 10:27:29 -0700
Subject: [PATCH 21/25] in send_message and open_message_stream, flatten
 to_addrs list

---
 lib/net/smtp.rb | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/net/smtp.rb b/lib/net/smtp.rb
index 3d0e37c..4e6719a 100644
--- a/lib/net/smtp.rb
+++ b/lib/net/smtp.rb
@@ -771,7 +771,7 @@ def do_finish
     def send_message(msgstr, from_addr, *to_addrs)
       raise IOError, 'closed session' unless @socket
       mailfrom from_addr
-      rcptto_list(to_addrs) {data msgstr}
+      rcptto_list(to_addrs.flatten) {data msgstr}
     end
 
     alias send_mail send_message
@@ -825,7 +825,7 @@ def send_message(msgstr, from_addr, *to_addrs)
     def open_message_stream(from_addr, *to_addrs, &block)   # :yield: stream
       raise IOError, 'closed session' unless @socket
       mailfrom from_addr
-      rcptto_list(to_addrs) {data(&block)}
+      rcptto_list(to_addrs.flatten) {data(&block)}
     end
 
     alias ready open_message_stream   # obsolete

From 86dcfa851625eab66583ab9a63ba10dfc8876ab0 Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Tue, 28 Mar 2023 10:43:21 -0700
Subject: [PATCH 22/25] rework rcptto_list, adding
 Net::SMTPMixedRecipientStatus exception

This change comes with some behavior changes:

* A new exception, SMTPMailboxPermanentlyUnavailable, can be thrown
  from any method that accepts a recipient address. It is a subclass
  of SMTPFatalError.
* A new exception, SMTPMixedRecipientStatus, can be thrown from
  `rcptto_list`. It is a subclass of SMTPMailboxPermanentlyUnavailable.
* In the event of all recipients being rejected by the server,
  previous versions of this gem would raise an `ArgumentError` that
  was indistinguishable from providing 0 recipient addresses. Now it
  will raise a more specific SMTP error.
* These exceptions are thrown *before* the method yields to the block.
  This allows the caller to inspect the exception and determine
  whether or not to continue with the transaction, instead.
---
 lib/net/smtp.rb | 92 ++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 72 insertions(+), 20 deletions(-)

diff --git a/lib/net/smtp.rb b/lib/net/smtp.rb
index 4e6719a..6704dd0 100644
--- a/lib/net/smtp.rb
+++ b/lib/net/smtp.rb
@@ -76,6 +76,21 @@ class SMTPMailboxPermanentlyUnavailable < ProtoFatalError
     include SMTPError
   end
 
+  # A synthetic status, raised from `rcptto_list`, when multiple recipients are given,
+  # and some have succeeded, but others encountered 501 (syntax error) or 55x (permanent
+  # mailbox error).
+  class SMTPMixedRecipientStatus < SMTPMailboxPermanentlyUnavailable
+    include SMTPError
+    attr_reader :ok, :permerror, :bad_syntax
+
+    def initialize(ok_addrs, permerror_addrs, bad_syntax_addrs)
+      @ok = ok_addrs
+      @permerror = permerror_addrs
+      @bad_syntax = bad_syntax_addrs
+      super("Mixed recipient status: #{@ok.length} ok, #{@permerror.length} permanent failure, #{@bad_syntax.length} bad syntax")
+    end
+  end
+
   # Unexpected reply code returned from server.
   class SMTPUnknownError < ProtoUnknownError
     include SMTPError
@@ -952,32 +967,69 @@ def mailfrom(from_addr)
       getok((["MAIL FROM:<#{addr.address}>"] + addr.parameters).join(' '))
     end
 
+    # +to_addrs+ is an +Enumerable+ of +String+ or +Net::SMTP::Address+
+    #
+    # Raises:
+    # * Net::SMTPSyntaxError
+    # * Net::SMTPServerBusy
+    # * Net::SMTPAuthenticationError
+    # * Net::SMTPMailboxPermanentlyUnavailable
+    # * Net::SMTPMixedRecipientStatus
     def rcptto_list(to_addrs)
       raise ArgumentError, 'mail destination not given' if to_addrs.empty?
-      ok_users = []
-      unauthenticated_users = []
-      permanent_error_users = []
+
+      # In the case of one recipient, pass it down to the plain rcptto (which
+      # will either succeed or raise one of the same exceptions that this method
+      # would have raised), yield to the block (which is expected to call data),
+      # and return early, so as to avoid having to carefully handle the
+      # single-recipient case here.
+      if to_addrs.length == 1
+        rcptto(to_addrs.first)
+        return yield
+      end
+
+      ok_addrs = []
+      unauthenticated_addrs = []
+      permanent_error_addrs = []
+      syntactically_invalid = []
+
       to_addrs.flatten.each do |addr|
-        begin
-          rcptto addr
-        rescue SMTPAuthenticationError
-          unauthenticated_users << addr.to_s.dump
-        rescue SMTPMailboxPermanentlyUnavailable
-          permanent_error_users << addr.to_s.dump
-        else
-          ok_users << addr
-        end
+        rcptto addr
+      rescue SMTPSyntaxError
+        syntactically_invalid << addr
+      rescue SMTPAuthenticationError
+        unauthenticated_addrs << addr
+      rescue SMTPMailboxPermanentlyUnavailable
+        permanent_error_addrs << addr
+      else
+        ok_addrs << addr
       end
-      raise ArgumentError, 'all recipients rejected by server' if ok_users.empty?
-      ret = yield
-      unless unauthenticated_users.empty?
-        raise SMTPAuthenticationError, "failed to authenticate for #{unauthenticated_users.join(', ')}"
+
+      # If any one of these addrs requires authentication, raise a specific error.
+      unless unauthenticated_addrs.empty?
+        addresses = unauthenticated_addrs.map { |addr| addr.to_s.dump }.join(', ')
+        raise SMTPAuthenticationError, "failed to authenticate for #{addresses}"
       end
-      # in this case there are mixed permanently-unavailable and OK recipients
-      unless permanent_error_users.empty?
-        raise SMTPMailboxPermanentlyUnavailable, "Recipient addresses failed: #{permanent_error_users.join(', ')}"
+
+      # If all recipients were accepted by the server, yield to the block, which
+      # is probably going to call `data` to deliver a message.
+      return yield if ok_addrs.length == to_addrs.length
+
+      # Now, we have eliminated all single-recipient cases, the successful case
+      # of all recipients being accepted, and the case of any number of
+      # authentication errors, so at this point there are any number of possible
+      # mixed permanently-unavailable, syntactically-invalid, and OK recipients.
+      # If all of the errors are of one type, raise a specific exception.
+      # Otherwise, raise SMTPMixedRecipientStatus.
+      if permanent_error_addrs.length == to_addrs.length
+        addresses = permanent_error_addrs.map { |addr| addr.to_s.dump }.join(', ')
+        raise SMTPMailboxPermanentlyUnavailable, "all recipients were permanently undeliverable: #{addresses}"
+      elsif syntactically_invalid.length == to_addrs.length
+        addresses = syntactically_invalid.map { |addr| addr.to_s.dump }.join(', ')
+        raise SMTPSyntaxError, "all recipients had syntax errors: #{addresses}"
+      else
+        raise SMTPMixedRecipientStatus.new(ok_addrs, permanent_error_addrs, syntactically_invalid)
       end
-      ret
     end
 
     # +to_addr+ is +String+ or +Net::SMTP::Address+

From dccfdf651233c1810b47bffbf9f6fff772c4df63 Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Tue, 28 Mar 2023 11:05:56 -0700
Subject: [PATCH 23/25] improve documentation

---
 lib/net/smtp.rb | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/lib/net/smtp.rb b/lib/net/smtp.rb
index 6704dd0..7875332 100644
--- a/lib/net/smtp.rb
+++ b/lib/net/smtp.rb
@@ -61,12 +61,12 @@ class SMTPServerBusy < ProtoServerError
     include SMTPError
   end
 
-  # Represents an SMTP command syntax error (error code 500)
+  # Represents an SMTP command syntax error (error code 50x)
   class SMTPSyntaxError < ProtoSyntaxError
     include SMTPError
   end
 
-  # Represents a fatal SMTP error (error code 5xx, except for 500, 53x, and 55x)
+  # Represents a fatal SMTP error (error code 5xx, except for 50x, 53x, and 55x)
   class SMTPFatalError < ProtoFatalError
     include SMTPError
   end
@@ -77,7 +77,7 @@ class SMTPMailboxPermanentlyUnavailable < ProtoFatalError
   end
 
   # A synthetic status, raised from `rcptto_list`, when multiple recipients are given,
-  # and some have succeeded, but others encountered 501 (syntax error) or 55x (permanent
+  # and some have succeeded, but others encountered 50x (syntax error) or 55x (permanent
   # mailbox error).
   class SMTPMixedRecipientStatus < SMTPMailboxPermanentlyUnavailable
     include SMTPError
@@ -967,7 +967,17 @@ def mailfrom(from_addr)
       getok((["MAIL FROM:<#{addr.address}>"] + addr.parameters).join(' '))
     end
 
-    # +to_addrs+ is an +Enumerable+ of +String+ or +Net::SMTP::Address+
+    # Submit a list of addresses to the SMTP server, handling common issues.
+    #
+    # Each address is protected against authentication errors (53x), syntax
+    # errors (50x), and mailbox permanent errors (55x); if all recipients
+    # encounter the same error, then an error of that type is raised. Otherwise,
+    # +Net::SMTPMixedRecipientStatus+ is raised.
+    #
+    # If all recipients are accepted, this method yields to a provided block,
+    # which can then call `DATA` to deliver a message.
+    #
+    # +to_addrs+ is an +Enumerable+ of +String+ or +Net::SMTP::Address+.
     #
     # Raises:
     # * Net::SMTPSyntaxError

From cbaedf31a5dec5e85de02a37a2e18372956005c4 Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Tue, 28 Mar 2023 11:07:58 -0700
Subject: [PATCH 24/25] make tests pass

---
 test/net/smtp/test_smtp.rb | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index c2f2db2..ea8e03d 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -591,7 +591,7 @@ def test_rcpt_to_bad_recipient
       port = fake_server_start
       smtp = Net::SMTP.new('localhost', port)
       smtp.start do |conn|
-        assert_raise Net::SMTPSyntaxError do
+        assert_raise Net::SMTPMixedRecipientStatus do
           conn.send_message "test", "me@example.org", ["you@example.net", "-friend@example.net"]
         end
       end
@@ -611,7 +611,7 @@ def test_rcpt_to_one_nonexistent_recipient_send_message
       port = fake_server_start
       smtp = Net::SMTP.new('localhost', port)
       smtp.start do |conn|
-        assert_raise Net::SMTPMailboxPermanentlyUnavailable do
+        assert_raise Net::SMTPMixedRecipientStatus do
           conn.send_message "test", "me@example.org", ["nonexistent@example.net", "friend@example.net"]
         end
       end
@@ -623,7 +623,7 @@ def test_rcpt_to_nonexistent_recipient_rcptto
       smtp = Net::SMTP.new('localhost', port)
       smtp.start do |conn|
         conn.mailfrom "me@example.org"
-        assert_raise Net::SMTPMailboxPermanentlyUnavailable do
+        assert_raise Net::SMTPMixedRecipientStatus do
           conn.rcptto_list ["friend@example.net", "nonexistent@example.net"] do end
         end
       end
@@ -647,7 +647,7 @@ def test_rcptto_list_all_nonexistent_recipients
       smtp = Net::SMTP.new('localhost', port)
       smtp.start do |conn|
         conn.mailfrom "me@example.org"
-        assert_raise ArgumentError do
+        assert_raise Net::SMTPMailboxPermanentlyUnavailable do
           conn.rcptto_list ["nonexistent1@example.net", "nonexistent2@example.net"] do end
         end
       end

From cd439ec4db8bceff714db949201ce0056288b8dd Mon Sep 17 00:00:00 2001
From: Alex Maestas <alex.maestas@zendesk.com>
Date: Tue, 28 Mar 2023 11:17:54 -0700
Subject: [PATCH 25/25] Make superclass of SMTPMailboxPermanentlyUnavailable as
 documented

---
 lib/net/smtp.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/net/smtp.rb b/lib/net/smtp.rb
index 7875332..779bcf1 100644
--- a/lib/net/smtp.rb
+++ b/lib/net/smtp.rb
@@ -72,7 +72,7 @@ class SMTPFatalError < ProtoFatalError
   end
 
   # Represents a fatal SMTP error pertaining to the mailbox (error code 55x)
-  class SMTPMailboxPermanentlyUnavailable < ProtoFatalError
+  class SMTPMailboxPermanentlyUnavailable < SMTPFatalError
     include SMTPError
   end