[TYPO3] extend htmlmail (Xclass or hooks?)

[Zachary Denison]

I need to extend the functionality of class.t3lib_htmlmail.php to
allow me to use an smtp server to send mail (on linux) - because php
on linux only lets you use sendmail (or a sendmail wrapper).

Rather than just edit the source file myself, and get it to work, I
would like to write some kind of extension because I am sure other
people would need this functionality.

What is the best way to go about this.  I think I can manage to do an
XCLASS extension but I have heard there is a new way to do extensions
with hooks.  Does anyone know where I would start to look, in order to
do a hook based extension of this class.

Thanks.