Trouble recieving email

[ScottChapman]

Well, I can send email just fine.

But incoming messages are just going into the deferred queue.

Can't really tell what the problem is since I can't view the entire error message in the admin UI.

Any ideas?

[ScottChapman]

OK. So, I unchecked DNS lookup on the MTA.

Any issues with that?

[mmorse]

First, is this a new problem and you were receiving mail fine before? Or is this still your first installation? (Like I assume based on thread location.)

I gather you mean un-checking DNS lookups helped.
While I know you're talking about incoming - do you use a relay for outgoing mail?
Incoming Mail Problems - Zimbra :: Wiki

An alternative to setting up a DNS server is to un-check "Enable DNS Lookups" on the MTA tab under Server configuration on the Zimbra Admin console. This requires a relay MTA to be configured somewhere that will accept all outbound email.

I see that your probably using a mailhop service (ISP blocking port 25) but don't actually state if you have implemented that yet.

Also see another thread by you on setting up a split dns - everything working properly with that? (What I suspect is not working.)

Another option is manual setting of zimbraMailTransport.

To check the reason they are differed examine your /var/log/zimbra.log or:
su - zimbra
mailq

(postsuper/postqueue commands are also helpful)

Fixed for 5.0.6: Bug 27537 - Mail Queue message informationr pop up does not work in 5.x