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"Connection refused" and "mail transport unavailable" errors appear when sending emails externally in InterScan Messaging Security Virtual Appliance (IMSVA)

    • Updated:
    • 21 Oct 2015
    • Product/Version:
    • InterScan Messaging Security Virtual Appliance 8.2
    • InterScan Messaging Security Virtual Appliance 8.5
    • InterScan Messaging Security Virtual Appliance 9.0
    • Platform:
    • N/A N/A
Summary

When you send emails to external domains, the following error messages show in the mail logs:

Connection refused

Connection refused in IMSVA

mail transport unavailable

Mail transport unavailable in IMSVA

Upon checking the Timestamp under the Log Query Details, you see the following:

Passed IMSVA scan and delivered, Bounced

Passed IMSVA scan and deliver, Bounced

Details
Public

Some external domains reject connections when there is an SMTP email address in the SMTP HELO command. The MTAs reponse to an email address in the HELO command varies. Microsoft SMTP server rejects it immediately, while Postfix accepts it. However, there are MTAs with stricter polices because "@" is not a valid character for a hostname or FQDN.

The SMTP requires MTA server to specify its hostname or FQDN in the HELO command, so stricter MTAs can really block emails with "@" character.

To resolve the issue:

  1. Login to IMSVA command line interface.
  2. Go to /opt/trend/mss/postfix/etc/postfix.
  3. Open the main.cf file.
  4. Ensure that the parameter below has no at sign (@). The default value should be "$myhostname" to use the actual value of "myhostname" parameter.

    smtp_helo_name=<mail server name>

  5. Save the changes.
  6. Restart the Postfix by running the commands:

    postfix stop
    postfix start

Premium
Internal
Rating:
Category:
Configure; Troubleshoot
Solution Id:
1099895
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