The Horrors of E-Mail
If you've ever wanted to send more than a basic email through PHP, or perform some processing on existing messages, then you might find my article in the May 2004 issue of php|architect a useful resource.
In the article, I provide you with a functional overview of the major RFCs, some hints on things to watch out for and tips on how best to do things to avoid your mail getting mangled in transit.