[GTALUG] Updating my mailserver

I have run a mailserver for my domains for a long time. I have not thought about its ability to send outbound mail for a while though, and my logs tell me what my experience already suggested - it cannot send email to Gmail (and probably lots of other places). Can anyone recommend a tutorial for setting up my mailserver (I'm using postfix on Debian) so that Gmail and others will accept my mails? I am pretty sure there is reverse DNS that I don't have set up, but there are probably other details I don't know about too. Thanks!