SMTP send-only server

Assuming that the "other servers" are within your current linode, then that guide looks like it'll be fine (PHP will just use the sendmail-like binary provided by Exim). You may also want to set an appropriate reverse dns etc.

If the other servers are actually located elsewhere, then you'll need to set up relaying for those IP addresses (though, of course you'd need some way of sending the mail on those nodes, which would largely defeat the purpose in this case unless you have a common mount point).

I will be using a PHP Class that allows me to send email through a smtp transport. To be precise i will be using: http://framework.zend.com/manual/en/zen … mails.html">http://framework.zend.com/manual/en/zend.mail.multiple-emails.html .

So I would like to send the emails through, for example, smtp.example.com

So it's possible to do this with exim? I just need to configure the DNS?

I haven't used that class, but from a cursory glance it seems that it should be fine. Just configure Exim to act as a smarthost for your external server IP's.

From the api docs, it looks like zendmailtransport_smtp will accept an IP address, but if not, /etc/hosts may be simpler than full DNS. (Obviously, you'll still need MX records for those domains.)