How do I force mails stuck in mail queue (incoming) to finally deliver (pop3)?

All these senders have always worked before, suddenly past 2 days it has not worked well without any modifications made on my part. I just did a forced exim update and prior / after did "attempt to delivery mail.." as well. Nothing moved yet.

centos 4.3 / cpanel 10x stable
exim / mailman

When clicking on "delivery message now.." on any particular email I see something like this

Message 1GIHt9-0004Kk-BF is not frozen
delivering 1GIHt9-0004Kk-BF
LOG: MAIN
== me@mydomain.com R=virtual_user T=virtual_userdelivery defer (-22): mailbox is full (MTA-imposed quota exceeded while writing to tmp/1156979405.H947954P8726.host.domain.com)

Now I checked the quota and indeed it was full, but the strange part is I use pop3 so all mails
are downloaded automatically on a per minute basis. How can this be?