[Log Findings]

    Line   832: Feb 10 12:03:14 imsva1 postfix/smtp[42575]: warning: host imsva2.trendmicro.com[192.168.10.5]:25 replied to HELO/EHLO with my own hostname imsva1.trendmicro.com
    Line   833: Feb 10 12:03:14 imsva1 postfix/smtp[42575]: 559C58205D: to=<user@trendmicro.com>, relay=imsva2.trendmicro.com[192.168.10.5]:25, delay=2.2, delays=2.1/0/0.14/0, dsn=5.4.6, status=bounced (mail for trendmicro.com loops back to myself)

[Recommendation]

It is because the peer checks your HELO/EHLO name, it requires your HELO/EHLO name that can be queried on the DNS server. By default, postfix uses hostname for HELO/EHLO name.

When you change myhostname value, the mail will also bounced because both IMSVA .39 uses the same HELO/EHLO name which caused postfix to think that there is a loop.

To get around this issue, we need to make HELO/EHLO name can be queried on DNS (or ask peer to add the IMSVA into the whitelist to skip HELO/EHLO check). To make HELO/EHLO name that can be queried on DNS.
Option 1: Publish FQDN on DNS and make sure it can be resolved on DNS.
Option 2: Find an FQDN that can already be queried on DNS and set it to myhostname in main.cf but FQDN must meet the following:
-MUST Not be your email domain itself otherwise postfix thinks IMSVA is the final destination for your domain emails. 
-MUST not be the same as other MTAs (otherwise postfix may think there is a loop)