From email address

To answer my own question, I was able to change the 'from' address by going into the settings for my Gmail account and changing the 'send email as' setting to no-reply@xxx.com.

I would have thought this would be possible through the module settings.

The "From" header email address is whatever the sending module sets it to. For example, the Webform module allows you to specify the "From" address in a mail handler. PHPMailer SMTP won't change the header, it passes it through as requested.

You can do this in code using hook_mail_alter(), setting $message['headers']['From'] = 'no-reply@xxx.com';.

That said, Google might not allow you to send from a different email address than the one associated with the account, which means the From address will always be jeff@... You can check this by using a different SMTP server.

The envelope sender (the SMTP command "MAIL FROM") address is where bounce messages are sent. The recipient's mail server adds the "Return-path" header based on this address.