If you are using the PEAR:Mail php function to send emails from your server remember to set the localhost parameter (ie $params[“localhost”]=’yourhost.com’;). If you don’t set it then the originating server will be “localhost”. While this won’t stop the email being sent, spamassassin will mark the message as spam – not good if you want your emails to be received.
This little gotcha recently bit me. I hadn’t set the localhost parameter and only noticed when I had upgraded spamassassin and found my test emails ending up in my junk mail folder.
As for why you might want to use PEAR::Mail over the normal php mail() function the main reason is you can control which smtp server your mail is sent out over. This control is very useful if you are testing your system on one server and sending out the emails via another server.