Hello, I have a problem with one of my customers who tries to send me emails that mailcow systematically refuses. However, I have no problem with other customers who send me emails without problems.

When email1@clientdomaine.com sends me an email I get this error:

<myemail@domain.com>: host mail.sendemail.fr[75.119.***.**] said: 550 5.1.0
 <email1@clientdomaine.com>: Sender address rejected: User unknown in
 virtual mailbox table (in reply to RCPT TO command)
Reporting-MTA: dns; smtp-1.jabatus.fr
X-Postfix-Queue-ID: 72B37E01C1
X-Postfix-Sender: rfc822; email1@clientdomaine.com
Arrival-Date: Sun, 21 Jul 2024 14:13:06 +0200 (CEST)

Final-Recipient: rfc822; myemail@domain.com
Original-Recipient: rfc822;myemail@domain.com
Action: failed
Status: 5.1.0
Remote-MTA: dns; mail.sendemail.fr
Diagnosis-Code: smtp; 550 5.1.0 <email1@clientdomaine.com>: Sender
 address rejected: User unknown in virtual mailbox table

But when the email client2@clientdomain.com sends me an email I receive it without problems.

I whitelisted my client’s domain in mailcow but I still have this problem.

Mailcow is in version 2024-06c and it is the latest version.

Thank you in advance for your help

Do both clients have the same @domain?

Are the customer accounts configured on your Mailcow or do they have there own Mailserver? When yes check the Mx record of your client1 and the check if his IP/Mailserver is blacklisted.

When yes then you can try to whitelist his server.

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    IdrisK Yes it’s the same domain between two different addresses

      Check your postfix and rspamd logs…

      Did you accidentally create your customer’s domain in your mailcow (Email -> Configuration -> Domains)?

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