Email is not being delivered [SOLVED]

I followed the Using Postfix with Courier and MySQL on Ubuntu 9.10 (Karmic), but am having some trouble getting mail delivered.

I set up my domain and username in the database, but when I try to use mailx to send the welcome message, it does not get delivered (I assume it should show up under /home/vmail, is that correct?).

I took a look at the /var/log/mail.log log and found the following:

Feb 23 03:11:39 localhost postfix/pickup[1216]: 7498B104BF: uid=0 from= <root>Feb 23 03:11:39 localhost postfix/cleanup[1392]: 7498B104BF: message-id=<20100223031139.7498B104BF@mydomain.com>
Feb 23 03:11:39 localhost postfix/qmgr[21034]: 7498B104BF: from=<root@mydomain.com>, size=321, nrcpt=1 (queue active)
Feb 23 03:11:39 localhost postfix/trivial-rewrite[1395]: warning: do not list domain mydomain.com in BOTH mydestination and virtual_mailbox_domains
Feb 23 03:11:39 localhost postfix/local[1396]: 7498B104BF: to=<daniel@mydomain.com>, relay=local, delay=0.05, delays=0.03/0.01/0/0.01, dsn=5.3.0, status=bounced (Command died with status 127: "procmail -a "$EXTENSION"". Command output: sh: procmail: not found )
Feb 23 03:11:39 localhost postfix/cleanup[1392]: 7CE15104C0: message-id=<20100223031139.7CE15104C0@mydomain.com>
Feb 23 03:11:39 localhost postfix/bounce[1399]: 7498B104BF: sender non-delivery notification: 7CE15104C0
Feb 23 03:11:39 localhost postfix/qmgr[21034]: 7CE15104C0: from=<>, size=2062, nrcpt=1 (queue active)
Feb 23 03:11:39 localhost postfix/trivial-rewrite[1395]: warning: do not list domain mydomain.com in BOTH mydestination and virtual_mailbox_domains
Feb 23 03:11:39 localhost postfix/qmgr[21034]: 7498B104BF: removed
Feb 23 03:11:39 localhost postfix/local[1396]: 7CE15104C0: to=<root@mydomain.com>, relay=local, delay=0.01, delays=0/0/0/0, dsn=5.3.0, status=bounced (Command died with status 127: "procmail -a "$EXTENSION"". Command output: sh: procmail: not found )
Feb 23 03:11:39 localhost postfix/qmgr[21034]: 7CE15104C0: removed</root@mydomain.com></daniel@mydomain.com></root@mydomain.com></root>

So it looks to me like it's not finding the users I set up and is bouncing the mail.

I'm pretty new at this stuff, I'd appreciate any help you can give! :)

(If it matters, my domain is not pointing to my Linode IP yet, but I did add mail.mydomain.com to my /etc/hosts file – it doesn't look like it's trying to use the old mail server though because daniel@mydomain.com is a functioning email address there so shouldn't be bouncing)