Long delay in sending mail

[rgrignon at INPHACT.COM]

We are running postfix 2.0.12 and MailScanner 4.21-9

I am noticing for the most part that mail is queued and delivered right
away, however, about 5-6 times a day the queue builds up and does not send.
It looks like it will eventually send within 15min, however, I am curious to
know what is causing MailScanner (or postfix) to eventually send the mail.

Is there some sort of cron job or a setting that I could adjust to force the
mail to be delivered in the event that the system hangs like it is currently
doing?

Thanks,

Rob