mail: use smtp under another user?

[doug_stevens]

I just installed mantis in Ubuntu 14.04.4 LTS, and everything is working very nicely except email (I'm running as admin until I can get that going).
The registration emails have been sent by mantis, as user www-data, but these are piled up in /var/spool/postfix/deferred.
"postqueue -p" reports that SASL authentication failed at the mail server.
There's only SASL user:password set for that server in /etc/postfix/sasl_passwd, for another user (ie, not www-data). Let's call that user "bob".

I don't have admin privileges to add another user to the mail server, but I do have sudo privileges on the machine that has mantis installed.
Is there a way to cause mantis to "su bob" before it sends the mail?

[doug_stevens]

Or could someone point me to the section of the mantis code that sends mail? Then I can modify it to add the "su bob" operation.

[atrol]

You could replace mail/sendmail by a shell.