* invoke mailer defaults as procs only if they are procs, do not convert
with to_proc. That an object is convertible to a proc does not mean it's
meant to be always used as a proc. Fixes #11533
*Alex Tsukernik*
Please check [4-0-stable](https://github.com/rails/rails/blob/4-0-stable/actionmailer/CHANGELOG.md) for previous changes.