Where is located the main.cf file in the Trend Micro InterScan Messaging Security Virtual Appliance v.8.5

After installation the new mail gateway IMSVA 8.5 I've noticed that some mail servers have rejected my messages with the next logs:
host  [X.X.X.X] said: 550 5.7.1 >: Helo command rejected: Host not found (in reply to RCPT TO command)

I thought there is problem with PTR-record, but it's OK. My mate helped me to find the main reason.

Problem occurs because my IMSVA uses its own hostname for invitation with other mail servers and this hostname is different from hostname registered for its MX-record. 
For example:
Hostname imsva85.domain.com
MX-record smtp2.domain.com

There is two way to solve this problem - change hostname or find solution inside mail service.
I decided to leave internal hostname and tried to find another way.
As all probably know IMSVA based on the POSTFIX system. I'd installed and managed the postfix systems few year ago and this experience helped me. But I couldn't find postfix's files in the ordinary folder /etc/postfix. I've connected with WinSCP and searched the main.cf file. File was found here /opt/trend/imss/postfix/etc/postfix
Original part of this file described bellow:

# INTERNET HOST AND DOMAIN NAMES

#

# The myhostname parameter specifies the internet hostname of this

# mail system. The default is to use the fully-qualified domain name

# from gethostname(). $myhostname is used as a default value for many

# other configuration parameters.

#

#myhostname = host.domain.tld

#myhostname = virtual.domain.tld

# The mydomain parameter specifies the local internet domain name.

# The default is to use $myhostname minus the first component.

# $mydomain is used as a default value for many other configuration

# parameters.

#

#mydomain = domain.tld

I've added one string about the MX-record, and now this part looks like this:

# INTERNET HOST AND DOMAIN NAMES

#

# The myhostname parameter specifies the internet hostname of this

# mail system. The default is to use the fully-qualified domain name

# from gethostname(). $myhostname is used as a default value for many

# other configuration parameters.

#

#myhostname = host.domain.tld

#myhostname = virtual.domain.tld

myhostname = smtp2.domain.com

After that file main.cf was saved and virtual server was stopped through CLI-mode. 

After restarting mail service works perfectly and problem is gone.