Very nice. Thx. This fixes the compatibility. Since there is check for the delivery_handler, I don't feel very bad about usa of the unsafe_load.

Since there is check for the delivery_handler, I don't feel very bad about usa of the unsafe_load.

Hm, this is probably not very relevant 🙄 Nevertheless, how about:

$ git diff
diff --git a/lib/mail/yaml.rb b/lib/mail/yaml.rb
index c0910855..b70da033 100644
--- a/lib/mail/yaml.rb
+++ b/lib/mail/yaml.rb
@@ -2,15 +2,23 @@ require 'yaml'
 
 module Mail
   module YAML
-    # unsafe loading compatible with Psych 3.x and Psych 4.x
-    if ::YAML.respond_to?(:unsafe_load)
-      def self.load(yaml)
-        ::YAML.unsafe_load(yaml)
-      end
-    else
-      def self.load(yaml)
-        ::YAML.load(yaml)
-      end
+    def self.load(yaml)
+      ::YAML.load(yaml, :permitted_classes => [
+        Symbol,
+
+        Mail::Body,
+
+        # Delivery methods as listed in mail/configuration.rb
+        Mail::SMTP,
+        Mail::Sendmail,
+        Mail::Exim,
+        Mail::FileDelivery,
+        Mail::SMTPConnection,
+        Mail::TestMailer,
+        Mail::LoggerDelivery,
+
+        Mail.delivery_method.class,
+      ])
     end
   end
 end

Hey there @voxik thanks for the help on creating this. I just kicked off the workflows and looks like we have some failures on 1.9, 2.0, 2.2, 2.7 and latest. Can you take a quick look at those and see if we can fix those up? cc @deivid-rodriguez

Sorry I'm late to the party :) Happy to help get these 3.x PRs resolved and merged and a new gem released asap.

My recall about current failures from working on #1472:

• The one on Ruby 2.7 is an existing flaky failure that happens randomly on different rubies. Restarting should "fix it".
• The failures on older rubies I think are already happening on master, and Add Ruby 3.1 support #1472 is dropping support anyways.

So I think this PR should be fine!

@mikel I unified changes from #1472 and this PR to get a base green CI at #1478. It would make this PR unnecessary (I kept proper attribution to @simi and @voxik at #1478).

Then I can rebase #1472 to take care of adding Ruby 3.1 support.

What do you think?