undefined method `eager_autoload!' for Mail:Module about mail

[chitty]

We also ran into this issue, and found it was caused by the incorrect file permissions in 2.8.0 bug. Pinning mail version to 2.7.1 fixed it.

[thekendalmiller]

We were also hitting this. While troubleshooting, the error would match the original post above, but also sometimes it would be

[29716] Early termination of worker
[29719] ! Unable to start worker
[29719] uninitialized constant Mail::TestMailer
Did you mean?  SystemMailer
[29719] /var/app/bundle/ruby/2.7.0/gems/actionmailer-6.1.7/lib/action_mailer/delivery_methods.rb:42:in `<module:ClassMethods>'
    /var/app/bundle/ruby/2.7.0/gems/actionmailer-6.1.7/lib/action_mailer/delivery_methods.rb:40:in `<module:DeliveryMethods>'
    /var/app/bundle/ruby/2.7.0/gems/actionmailer-6.1.7/lib/action_mailer/delivery_methods.rb:8:in `<module:ActionMailer>'
    /var/app/bundle/ruby/2.7.0/gems/actionmailer-6.1.7/lib/action_mailer/delivery_methods.rb:5:in `<top (required)>'
    /var/app/bundle/ruby/2.7.0/gems/zeitwerk-2.6.6/lib/zeitwerk/kernel.rb:38:in `require'
    /var/app/bundle/ruby/2.7.0/gems/zeitwerk-2.6.6/lib/zeitwerk/kernel.rb:38:in `require'
    /var/app/bundle/ruby/2.7.0/gems/actionmailer-6.1.7/lib/action_mailer/base.rb:438:in `<class:Base>'
    /var/app/bundle/ruby/2.7.0/gems/actionmailer-6.1.7/lib/action_mailer/base.rb:437:in `<module:ActionMailer>'
    /var/app/bundle/ruby/2.7.0/gems/actionmailer-6.1.7/lib/action_mailer/base.rb:12:in `<top (required)>'
    /var/app/bundle/ruby/2.7.0/gems/zeitwerk-2.6.6/lib/zeitwerk/kernel.rb:38:in `require'
    /var/app/bundle/ruby/2.7.0/gems/zeitwerk-2.6.6/lib/zeitwerk/kernel.rb:38:in `require'
    /var/app/current/app/mailers/application_mailer.rb:1:in `<top (required)>'

ruby 2.7.7
rails 6.1.7
mail 2.8.0

[eval]

Closing as this was related to the permission problem which is fixed as of v2.8.0.1.