Outlook has stopped retrieving messages on 1 account

I have 7 POP accounts set up in Outlook for Mac 2011 on my iMac. Everything has worked fine for years, until yesterday. Outlook will no longer retrieve messages for 1 of my email accounts. It will send and receive fine on the other accounts, and it will even send mail on the problematic account. But when retrieving mail, it stalls at "Messages Received: 0 / X".

Nothing has changed. No settings have been adjusted, either in Outlook or with my mail host. There is nothing wrong with my mail server. I have other accounts on this same domain (it's my company domain) and they all work just fine. And I can access this "problem" account via webmail and retrieve messages on other devices like my phone and laptop just fine. 

I've tried deleting the account and re-adding it.

I've tried rebuilding the Outlook database.

I've tried repairing permissions on the iMac.

Nothing. It still stalls. Curiously, it also never times out or gives me an error message.

Any tips on fixing this?

Thanks!