I'm kind of a *NIX noob and I have a bunch of domains I want to administer email for. I set up Google Apps for incoming mail, using one account and lots of domain aliases, and it works fine. My only problem is with outgoing mail.

I want to be able to send email from a) Google Apps and b) PHP mail() scripts and have both show headers that match the right domain.

Right now I can send email from the main Google Apps domain and the headers are fine, but if I send from one of the domain aliases, there is a header linking it to that main domain, which I don't want (i.e. I don't want someone who receives a message from dog.com to be able to unpack the message headers and see that it is an alias of cat.com). I figure the way around this is to have a different SMTP server on my Linode for each domain I want to send from, but I have no idea of the simplest way to configure that. I've looked at different tutorials for Postfix and Exim but they all seem to assume that you only have one domain.

PHP mail() actually works by default right now even though sendmail_path isn't defined. I don't understand how that's possible, but oh well. I can set the "From:" header within the script, but the Received: headers still show the hostname "localhost." How can I get those to match different domains depending on which script is doing the sending?

Thanks for any ideas...