Mails are not delivered and you encounter a Non-Delivered Report (NDR) with the following error message on IMSVA 8.2:
DSN: Service unavailable
The email flows from the Internet to Third-party mail proxy to IMSVA 8.2 and to Internal mail server.
The NDRs are generated and sent by the third-party mail proxy. Upon checking the proxy’s mail log, you see the following:
Aug 27 15:31:44 spam sendmail[65984]: r7R7Vegi065984: to=, ctladdr=(0/65534), delay=00:00:04, xdelay=00:00:04, mailer=esmtp, pri=12608387, relay=[192.168.1.15] [192.168.1.15], dsn=5.0.0, stat=Service unavailable
However, the mail log on IMSVA shows error code 5.3.4 instead of 5.0.0:
Aug 27 15:31:44 imsva8 postfix/smtpd[20601]: NOQUEUE: reject: MAIL from unknown[192.168.1.200]: 552 5.3.4 Message size exceeds fixed limit; proto=ESMTP helo=
The third-party proxy translated an incorrect error code so the DNRs it generated are misleading.
The issue occurs because IMSVA rejects mails that exceeded the maximum message limit. The default maximum message size limit is 10 MB.
To resolve the issue, adjust the message size limit :
- On the IMSVA console, go to Administration > SMTP Routing > Message Rule.
- Under Maximum Message sizefield, increase the value. For example, 20 MB or higher.
- Click Save.
