Postfix server getting bogged down!

Greetings, as you can probably tell by reading my post, I am not the
greatest with postfix. I do have a problem that I cannot seem to
figure out. This has happened a couple times in the past few weeks.

What I see is outbound/inbound mail slows to a crawl. I will send a
message out and it could take hours to appear to an external mailbox.
Same thing for incoming mail.

When this happens the mailq is HUGE, thousands of emails. In
/var/spool/postfix the defer folder is over 2gigs, normally its next
to nothing. I see in the mailq many messages to a local email from
the same external host...but I dont know why it wouldnt be delivered.

Any idea where I should look? I looked in /var/log/maillog and see
many messages regarding the arrival of mail for the local account,
its says "Queue active" so I dont know if that is the problem or not.

Any help is appreciated.