Need a little mail server help

Short version is I need help figuring out why I'm getting this error message:

postfix/lmtp[12637]: 4DC4FC18C: to=<postmaster@example.com>, orig_to=<postmaster>, relay=server.example.com[private/dovecot-lmtp], delay=0.07, delays=0.03/0.01/0.01/0.01, dsn=5.1.1, status=bounced (host server.example.com[private/dovecot-lmtp] said: 550 5.1.1 <postmaster@example.com> User doesn't exist: postmaster@example.com (in reply to RCPT TO command))

Longer version is I followed this to the letter and while I can send mail I can't actually get any mail. I think I've traced it to the lmtp service but I'm stuck at that point. It's been a while since I've done anything with setting up a mail server so I'm really rusty... any and all help is appreciated.

Off topic, maybe, but I'm also having a couple config issues for SSL/TLS but I should be able to track those down after a bit of sleep. I doubt the issues are related but I thought I'd toss it out there just in case. I figure I just forgot to change an ssl cert in some config file - I'll be going through them tomorrow. Can you tell I'm exhausted?

Main reason I'm doing this, though not entirely, is I have an interview coming up soon and I wanted to go back through SMTP and Apache.

Using: Postfix, MySql, Dovecot, Apache, Squirrelmail (or at least trying to) all on a Linode Debain 7 server.