Icewarp Merak mail server not working behind a smtp relay

Just migrated an email server to a dedicated server at GoDaddy, and according to their policies, 25 TCP port is blocked "to prevent spam", and they force us to use their smtp relay for mail delivery.

After properly configuring all delivery related settings, server still could not send emails.

A quick look in smtp logs:

SYSTEM          [087C] 23:03:41 Client session ***   1 569 00:00:00 INCOMPLETE-SESSION ESZ92941
SYSTEM          [0BE8] 23:07:55 Client session ***   1 569 00:00:00 INCOMPLETE-SESSION ESZ92941

Strange.
Turned on debugging:

SYSTEM          [04C4] 23:42:26 Client session Message id ESO58526 item 200812232342260002.tm$
SYSTEM          [04C4] 23:42:26 Client session Connecting to 'smtprelay.server.net'
SYSTEM          [04C4] 23:44:26 Client session Could not connect to 'smtprelay.server.net(0.0.0.0)'

This "0.0.0.0" looked strange to me, it seems there was some issues with dns.
After a little digging in Merak's settings, it appears that actually the mail server does not use system default resolvers, and uses it's own.

Just adjusted dns settings in System>Internet Connection>Dns, it started to work like a charm