imail can’t deliver mail to internal exchange server

Having an issue where imail can’t deliver to an exchange server in house. Firewall recently replaced with a SonicWall, and I believe all rules are correctly applied. imail can deliver to everyone else and can receive mail from everyone including in house exchange server. Exchange server is able to receive and deliver to all. I believe it’s DNS related, can someone point me in the right direction. Thanks.

Please assume the following info

imail server – 2 network cards
card 1 – 192.168.0.200
card 2 – 192.168.10.240

exchange server – 1 network card 192.168.10.250