Before Rails 7.0 was released, neither the Mail gem or Rails were
providing a default timeout for SMTP, so there was a risk of processes
being stuck while sending emails.
That's no longer the case, though; we're using version 2.8.x of the Mail
gem, which already provides a default timeout [2].
Since the default timeout provided by the Mail gem is the same as the
default timeout provided by Rails 7.0, it doesn't matter whether we
enable this option. We're enabling because it's easier to just use the
default 7.0 configuration.
[1] Issue 41244 in https://github.com/rails/rails
[2] Pull request 1427 in https://github.com/mikel/mail
904a175541