I’m doing a bit of work writing a POP3/IMAP handler and here are some links I found mildly interesting in that search area.

How to protect from Spoofed/Forged Email

3d Traceroute FREE – the free version has an “eMail header analyser” at the page “Mail Header Analyzer.”

Win32 OpenSSL Installation Project – which reminds me, what SSL do I have?  Or rather, which SSL implementation do I have on my Windows host, Linux host, (Windows) development machine and PHP IDE that I believe also installs SSL certificates of some kind.

Email Header Injection in PHP – not really the most advanced topic but exactly what I need and that is a condensed version of what to look out for (I can expand the information as need be).

I did not find this per this particular search but recalled it being a great security demonstration by the super-PHP’er Tony Bibbs.

Examine e-mail headers to determine their real origin (TechRepublic)

WeberDev always has great articles but this one is a decade old in 10 days (talk about odd coincidence).  It looks promising though.

I could have just pointed you to the PHP Classes site so you could download the owner’s own POP3 e-mail client class, but this site was much funnier in pointing to it.

This is a completely useless snippet that breaks easily, but could be useful in simple scenarios for retrieving “the name” from an “e-mail address.”

“How to View Email Headers” may assault your eyes but it makes sure to flush your eyes with good information afterward.