How can I configure the email user that vBulletin uses?

[DarwinsMessenge]

I'm having problems getting emails from vBulletin to actually arrive at their destinations.
(3.8.4 PL2)

This message never arrives:

Originally Posted by maillog

Dec 27 14:57:38 ip-173-201-23-32 postfix/pickup[32237]: 0061F203AE6: uid=48 from=<apache>
Dec 27 14:57:38 ip-173-201-23-32 postfix/cleanup[32258]: 0061F203AE6: message-id=<20091227215737.30009334afa6@173.201.23.32>
Dec 27 14:57:38 ip-173-201-23-32 postfix/qmgr[32236]: 0061F203AE6: from=<apache@ip-173-201-23-32.ip.secureserver.net>, size=519, nrcpt=1 (queue active)
Dec 27 14:57:42 ip-173-201-23-32 postfix/smtp[32316]: 0061F203AE6: to=<pdx_vw_erik@hotmail.com>, relay=s2smtpout.secureserver.net[208.109.80.210]:25, delay=4.1, delays=0.06/0/4/0.06, dsn=2.0.0, status=sent (250 Accepted message qp 10259 bytes 693)
Dec 27 14:57:42 ip-173-201-23-32 postfix/qmgr[32236]: 0061F203AE6: removed

This message does (sent from the command line manually):

Originally Posted by maillog

Dec 27 17:01:59 ip-173-201-23-32 postfix/pickup[1400]: 37182203AE6: uid=500 from=<oferik>
Dec 27 17:01:59 ip-173-201-23-32 postfix/cleanup[32302]: 37182203AE6: message-id=<20091228000159.37182203AE6@ip-173-201-23-32.ip.secureserver.net>
Dec 27 17:01:59 ip-173-201-23-32 postfix/qmgr[32236]: 37182203AE6: from=<oferik@ip-173-201-23-32.ip.secureserver.net>, size=356, nrcpt=1 (queue active)
Dec 27 17:02:03 ip-173-201-23-32 postfix/smtp[32305]: 37182203AE6: to=<pdx_vw_erik@hotmail.com>, relay=s2smtpout.secureserver.net[208.109.80.210]:25, delay=8.3, delays=3.8/0.01/4.5/0.06, dsn=2.0.0, status=sent (250 Accepted message qp 13109 bytes 536)
Dec 27 17:02:03 ip-173-201-23-32 postfix/qmgr[32236]: 37182203AE6: removed

Godaddy tells me that they can't see any problems and their outgoing server isn't blocking anything. They suggest that I change the user that vBulletin uses to send emails with.

Is it a vBulletin thing or an Apache thing? If it's a vBulletin thing, how do I configure the user that it's using to send emails with? If it's an Apache thing, does someone know how I can change that?

TIA,

Erik