sql-server-2005 - SQL Server 2005 DbMail not sending

Question

I have a SQL Server 2005 DB Mail profile set up on my server that successfully sends a test email. However, when I queue an email in the msdb.dbo.sysmail_mailitems table, it does not ever try to send it. The status of the item stays at 0 (unsent).

In the Database Mail Log, the following entries are shown:

event_type  log_date                description                             process_id  mailitem_id  account_id  last_mod_date              last_mod_user
0           2012-05-07 10:07:00.887 Activation successful.                  NULL        NULL         NULL        2012-05-07 10:07:00.887    sa
1           2012-05-07 10:07:06.323 DatabaseMail process is started         6504        NULL         NULL        2012-05-07 10:07:06.323    NT AUTHORITY\SYSTEM
3           2012-05-07 10:07:07.213 Could not retrieve item from the queue. 6504        NULL         NULL        2012-05-07 10:07:07.213    NT AUTHORITY\SYSTEM
1           2012-05-07 10:12:07.453 DatabaseMail process is shutting down   6504        NULL         NULL        2012-05-07 10:12:07.453    NT AUTHORITY\SYSTEM

There are no exceptions in the windows event viewer. Can someone direct me to where I can find more info regarding the error? "Could not retrieve item from the queue." doesn't help me much.

Thanks