A couple of days ago, however, all of a sudden my inbox displayed the following message, even though there were plenty of messages both read and unread in the folder:

There are no messages in this mailbox.

The funny thing was, I could see all of the messages in the folder if I did a search for a string that was not found – for example search for messages in inbox from “nosuchuser”:

Some searching revealed that others have occassionally seen a similar problem, and there seemed to be a connection to the IMP preferences for the user having the problem. The most common recommended solution was to delete all of the imp preferences for the user.

Since I have a lot of customized settings, I wanted to avoid that if possible, so I went digging. I tracked the problem down to a garbled setting in the sortpref preference setting. The solution for me was to reset sortpref to its’ default setting. I did this with the following SQL code:

update horde_prefs set pref_value=’a:0:{}’ where pref_uid=’USERNAME‘ and pref_name=’sortpref’ and pref_scope=’imp’;

(Of course, you have to replace USERNAME with the actual username of the user having the problem)

After logging out and back in again, the problem was fixed.

- Source