I have a server setup to use exim4 and google apps as my smarthost. But I get errors when the to address is not the one I use to authenticate to google and it seems to drop all return addresses that are not the one it uses to authenitcate.

Example: On the contact form of my server a user sets [email protected] as their return address and uses the form to send a message.

I get an email sent to the admin's address [email protected] but the return address is also now [email protected] I have no idea of the return address the user set on the form.

I get around this by putting a bad email address in the form's default so Exim4 sends an error message to [email protected] with the user's email in the debug info.

Clearly I either have it set up wrong or do not understand how smarthosts work (probably both).