This moves a step closer to having a simple and straightforward way to
configure the app's mail delivery which doesn't require to be a nuclear
engineer to troubleshoot mail issues.
It happens way too often that servers have mail config broken when
restarted or redeployed and it takes too much brain power to fix it. No
doubt; it's way too complex.
I chose to leave this page's form fields but "Send mails as" as
read-only. This other field is still used by instance manager to
troubleshoot mail issues.
