Got the following error when I tried the Mailhandler module to retrieve the email:

imap_open(): Couldn’t open stream {mydomain.com:110/pop3} in /home/applications/drupal-4.6.3/modules/mailhandler.module on line 17

This will happen if your mailserver support SSL / TLS / STARTTLS. It seems that Mailhandler got confused.

In this case, you’ll need to append the /pop3 above with /notls.
So it’ll become /pop3/notls

To edit it, open drupal/modules/mailhandler.module,
go to line 15,
and modify as I mentioned above.

Afterwards it’s able to retrieve email as normal.

UPDATE:
Turned out there’s an easier way (duh), here it goes:

1. Login to your Drupal site
2. Choose administer - mailhandler
3. Click any mailbox’s EDIT link
4. Scroll down a bit, there’ll be a setting called EXTRA COMMANDS. Put /notls in there
5. Scroll to the bottom, click on SUBMIT
6. Go back to point #3, and go through all the mailboxes