XG Mail Config in MTA Mode

Question

Hi all, 
 we have a XG (SFOS 18.4) with Mailconfig in MTA mode (which is necessary). 
 There is now one private network behind the XG that should skip the MTA and forward mails directly to another mail host in the internet. 
 So how to skip the MTA responding n port 25 to that network? 
 A telnet on port 25 to the mailserver in the internet forces actually the local MTA to answer. 
 Any hint? Thanks!

HardikR · Answer

Create firewall rule on top(above default MTA rule) with source as private network that need to be skipped and destination as Any with service as SMTP and do not apply smtp scanning in this rule.