Revert "DEV: Drop our `mail` gem fork (#16622)" (#16853)

This reverts commit 0d30c19b7e.

Pending resolution of https://github.com/mikel/mail/issues/1489

Gemfile

@@ -41,7 +41,7 @@ gem 'actionview_precompiler', require: false
 
 gem 'seed-fu'
 
-gem 'mail', '2.8.0.rc1', require: false
+gem 'mail', git: 'https://github.com/discourse/mail.git', require: false
 gem 'mini_mime'
 gem 'mini_suffix'
 

Gemfile.lock

@@ -1,3 +1,10 @@
+GIT
+  remote: https://github.com/discourse/mail.git
+  revision: 5b700fc95ee66378e0cf2559abc73c8bc3062a4b
+  specs:
+    mail (2.8.0.edge)
+      mini_mime (>= 0.1.1)
+
 GEM
   remote: https://rubygems.org/
   specs:
@@ -221,11 +228,6 @@ GEM
       nokogiri (>= 1.5.9)
     lru_redux (1.1.0)
     lz4-ruby (0.3.3)
-    mail (2.8.0.rc1)
-      mini_mime (>= 0.1.1)
-      net-imap
-      net-pop
-      net-smtp
     maxminddb (0.1.22)
     memory_profiler (1.0.0)
     message_bus (4.2.0)
@@ -563,7 +565,7 @@ DEPENDENCIES
   loofah
   lru_redux
   lz4-ruby
-  mail (= 2.8.0.rc1)
+  mail!
   maxminddb
   memory_profiler
   message_bus