Troubleshooting Tip: Recipient verification failed with 'user unknown' in the FortiMail logs

[vchauhan]

Description	This article describes how to resolve an issue where the recipient verification failed and an unknown user is indicated in the FortiMail logs.
Scope	FortiMail.
Solution	Example: column Content Date      2023-11-01 Time     03:02:25.181 Message             <user2@lab.la>... User unknown Session ID          3A1A1dcI002181-3A1A1dcJ002181 Verify if the user exists on the backend server by telnetting the SMTP server. For example: execute telnettest 10.109.20.132:25 Connected  220 FEVM010000225947.localdomain ESMTP Smtpd; Wed, 1 Nov 2023 03:01:39 -0700  Entering interactive mode. Type CTRL-D to exit. 250-FEVM010000225947.localdomain Hello [10.109.22.47], pleased to meet you 250-ENHANCEDSTATUSCODES 250-PIPELINING 250-8BITMIME 250-SIZE 10485760 250-STARTTLS 250-DELIVERBY 250 HELP mail from: <admin@test.com> 250 2.1.0 <admin@test.com>... Sender ok rcpt to: <user2@lab.la> 550 5.1.1 <user2@lab.la>... User unknown Connection closed. If the user exists: 250-FEVM010000225947.localdomain Hello [10.109.22.47], pleased to meet you 250-ENHANCEDSTATUSCODES 250-PIPELINING 250-8BITMIME 250-SIZE 10485760 250-STARTTLS 250-DELIVERBY 250 HELP mail from : <admin@test.com> 250 2.1.0 <admin@test.com>... Sender ok rcpt to:<user1@lab.la> 250 2.1.5 <user1@lab.la>... Recipient ok Connection closed.