[Hellcat]

Using PHP's mail() function has a downside for this:
It sends the mail over YOUR server. Depending on your config your server won't allow that and some more problems that might arise.

Using the IMAP function has the (IMO mayor) downside of needing the IMAP libraries compiled into PHP (not everyone has those, incl. me )

[EDIT]
I just found a detailed example "dialog" Mail-Client <-> SMTP-Server on Wikipedia.
Perfect, now I can modify my "LOGIN" auth method based on this.

The "LOGIN" auth method is the one we need!
And it's almost correctely implemented, I just need to send a "EHLO" instead of a "HELO" at the beginning.
Yay,
[high]* Hellcat checks....[/high]