I have an IMAP problem, cannot be accessed from outside office, but can be accessed from inside office.
Our firewall already setup to accept the IMAP port, 143 and 993, and I have check from outside network (from public internet) that the firewall is already listening to those ports.
Our user from internal network have no problem connecting to their zimbra mailbox using IMAP (Thunderbirds). But failed to connect from external network (internet network).
There is no connection problem between zimbra server and the firewall.
Any idea where I should look in to find the cause?