recently installed monowall and configured the dmz, put the mailserver and
two webservers on it, i also made an override in the dns forwarder so that
LAN users will be able to login to the mailserver and visit the website,
however i failed to test if users will still be able to login to mailserver
via its squirrelmail interface or via the websites login page, and to my
surprise users can't login to the mailserver, they always get a connection
timeout error, mail taking too long error on the browser. i advised them to
use the internal ip of the mailserver for the time being and whoola, they
can log in via the internal ip.
why is this? what configuration do i have to edit so that this error will
not occur again.

TIA