I am getting this error when sending to domain@domain.com that’s set up with Microsoft Exchange, so the receiving end should be fine, all SPF, DMARC, etc is done for the domain sending as well.
Also, it doesn’t even TRY to send, it’s INSTANT as soon as I hit the button, if I hit it fast enough it will actually say connection error under the error.
How can a server be restricted from sending to a custom domain that’s set up within exhange? Not only that, the A records for BOTH domains USE THE SAME SERVER, it’s only MX SPF DMARC that are email@exhange.com and then everything from A-AAAA-MX etc SPF DMARC for other@domain that’s sending gets this error.
I was able to send with no issue to @gmail@yahoo@live (Microsoft) @yahoo etc with no issue
I too had this problem (posted recently) following an update (sadly not resolved or understood by me) good luck - I think it has something to do with some Postfix setting.
At some point there was discussion about format for the usernames in roundcube and I think there was an option to add an extra alias for roundcube. I think it had to do with the handling the “@” symbol or the way it was escaped or some such whatever.
Does it work from Usermin? That might be a clue. Though you do get logged into Roundcube OK? Hmm…
You might search the forum for that.
From /etc/postfix/virtual
mittens@tions.com mittens\@tions.com
EDIT: Just realized the software removed the escape character.
You need to post the mail log when you hit send.
5.1.1 is basically the receiving mail server rejecting the email due to the user not being known as you see in the error.
Roundcube still uses postfix to send and you should see this in the mail log.
DMARC really doesn’t effect this, its a user unknown error.
