IMAP not synchronizing on clients

Hi,

For the last several days, my IMAP clients are not properly synchronising with Zoho Mail.

I can see new messages coming on the zoho mail web ui and I get them on iPad/iPhone but my inboxes on the desktop computers are not getting the messages.

Happens on Mail for Mac OS X and sometimes it takes DAYS to get in sync again.

Mail is not reporting any connectivity issues at all.