How to fix "Recipient address rejected: Domain not found" [Kaspersky Secure Mail Gateway]

[Antipova Anna]

Advice and Solutions (Forum Knowledgebase) Disclaimer. Read before using materials.

Issue

During initial deployments you may encounter errors like this:

Jun 3 12:50:13 ksmg postfix/smtpd[841]: NOQUEUE: reject: RCPT from ksmg.example.com[10.10.10.1]: 450 4.1.2 <test@example.com>: Recipient address rejected: Domain not found; from=<test@example.com> to=<test@example.com> proto=ESMTP helo=<example.com>

This means that the recipient domain could not be verified in DNS.

Solution

There are multiple ways to avoid it:

• create a proper DNS records for the mentioned domain on the DNS server that is used by KSMG
• configure to use a different DNS server that has proper records
• just disable this check in Settings -> MTA -> Advanced Settings -> Reject messages for unknown recipient domains

When that check is enable, requests are rejected, when the RCPT TO domain has

• no DNS MX and no DNS A record
• a malformed MX record (a record with a zero-length MX hostname)