Can't send e-mail from a user - Sender Address rejected not owned by user:

I setup mail in a box with two domains. on the 2nd domain I added I receive:

An error occurred while sending mail. The mail server responded: 5.7.1 <>: Sender address rejected: not owned by user Please check the message recipient "" and try again.

If you setup as an alias that points to it should allow it. Having them setup as two separate users though, won’t. This is to prevent one user from sending and pretending to be another user that s/he isn’t allowed to.

Had the same problem today.
If you are using Mozilla Thunderbird, it could be a problem with your Outgoing Server (SMTP) Settings. is probably trying to use the default outgoing server from So you will need to set the default outgoing server to a different address.

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