Well, it occurs to me that there must be quite of few people who have written code like this, so a search reveals:
- PHP: mailparse functions - Manual. These are some routines from the main PHP server itself that let's you parse the entire stream. Pretty useful like mailparse_rfc822_parse_addresses. Not super well documented, but about what I need.
- Pear Mail_RFC822 Parsing. This is from PEAR, an application library for PHP. Seems to do a similar thing to be downloaded from Pear Packages