Users are unable to send outbound mails via IMSVA:
<Recipient_address>: host <recipient_host> said: 450 4.7.1 : Helo command rejected: Host not found (in reply to RCPT TO command)
The error "Helo command rejected: Host not found" is returned by the downstream MTA, and it means downstream MTA rejected the SMTP connection because it cannot resolve host name in the SMTP HELO command.
The following is a workaround to resolve such errors:
Backup and then edit main.cf file.
#cp main.cf main.cf.backup
Set "myhostname" to a publicly resolvable FQDN, usually you should use the reverse DNS lookup result of your public IP:
Change from "#myhostname = host.domain.tld" to "myhostname = your_domain_reverse_dns_lookup_result" (on impacted server).
Save and restart service.
#sh /opt/trend/imss/script/imssctl.sh restart
If the workaround does not work, please rollback the change and contact Trend Micro Technical Support.