Startup script question

[Levin]

Hi,

My mailbox running a sendmail MTA as a relay-only gateway, I setup a 
mailscanner up and run, however I found out that if it state 
DeliveryMode=queueonly  in /etc/rc.d/init.d/MailScanner script, all 
incoming from from otherworld will stuck into /var/spool/mqueue.in and 
not go anywhere, also /var/log/maillog show the mail was queued NOT 
sent, so I modify it to DeliveryMode=background, it seems work... but I 
don't know anything wrong, would you please describe a little bit my 
statement?

Thank you very much!

Levin