i'm having problem with one of the domain's emails. all emails going to the inboxes seems to be qued and not sending at all. the rest of the domains in my server seems to be working fine. i even tried the option "Attempt to Deliver all messages in Queue" and it didnt work. anyone have any ideas what's going on?

Few things to check.

1: Check to see if the email accounts exsist
2: Use the rebuild mailboxes on the emails tab in WHM
3: If the email accounts exsist, perhaps they are full
4: Do you have spam rules set in Spam assassin? I have seen a bad rule block all emails to accounts before