User unknown in relay recipient table


Have searched the forum but can’t find an answer to my problem.

I’ve successfully installed mail-in-a-box and it works sending/receiving mails using the domain After that I added a user to another domain,, and fixed all DNS-settings. All system status checks are now green for both domains.

It works fine sending mail from, but when I try to send a reply from my desktop mail client (Thunderbird) I get this error:
“An error occurred while sending mail. The mail server responded: 5.1.1 Recipient address rejected: User unknown in relay recipient table.”

Now I can’t figure out what is wrong, since the recipient address is listed in the user list. Please give me some directions…

What SMTP server is your desktop mail client using? (The Mail-in-a-Box or something else?)

Is that user you are sending email to have a different username than “”?

According to the answer @ Postfix: Recipient address rejected: User unknown in local recipient table, even though recipient domain is an external domain - Server Fault This can happen when postfix is receiving email for but the users actual domain is domain2.tld (or domain2.local, etc, it’s just DIFFERENT than the actual domain name)

I’m using a different SMTP for my desktop mail client, so it’s another mail server that is reporting the error.

Update 1:
It does work for the account to mail itself. Also I could send a mail to the account from my gmail-account, so it might be my other SMTP (used it for years) that is doing something strange.

Update 2:
Finally solved it. The problem was that the SMTP I was sending with belonged to the same ISP where I had my old DNS-settings for the domain (before changing the name server). The SMTP used those old settings instead of recognizing the new name server (mail-in-a-box). It turned out that all other SMTPs except my own could send mails to the account.

Thanks for all help. Hope this might point someone else in the same direction.

Yes, it’s a valid mail account on mail-in-a-box. All system status checks are ok for the domain. I just anonymized it.

Will need to look closer at the link you supplied. Wasn’t obvious to me right away…

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