Mail fail x-unix; can't create user output file

with a new user created it username is “admin@domain”… though on another server it is “admin.domain” I don’t get why that is… but anyway trying to send emails to this email address is failing for whatever reason…

I had problems on the other server with creating an catch all admin@<domain> account… I don’t get why virtualmin doesn’t specifiy the email address we want creating by default tbh … like who wants <domain>@<domain> as an email address …just something I have to go in a remove all the other additional mailboxes it catches… and then create another email… .

anyway besides it seems by default setup this stuff is a bit broken… thunerbird was balking at the username not being correct until I ran the command “virtualmin config-system --include SASL” which then seemed to fix that server… but now this server is having trouble getting any emails to the admin@ account… see below error…

just dont’ get it… all I’ve done is clean server and install virtualmin and do everything to set it up in the web admin… not touched any server files… but it seems something is wrong in the script setup somewhere…??? please help thanks… its doing my head in trying to fix this.

|Operating system|Ubuntu Linux 22.04.3|
|Webmin version|2.101|
|Usermin version|2.001|
|Virtualmin version|7.7|

This is the mail system at host sys16.<domain>.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

<"admin@<domain>"@sys16.<domain>> (expanded from
    <admin@<domain>>): can't create user output file


Reporting-MTA: dns; sys16.<domain>
X-Postfix-Queue-ID: 8EA021EC18F2
X-Postfix-Sender: rfc822; a---
Arrival-Date: Thu,  7 Sep 2023 13:57:06 +0000 (UTC)

Final-Recipient: rfc822; "admin@<domain>"@sys16.<domain>
Original-Recipient: rfc822;admin@<domain>
Action: failed
Status: 5.2.0
Diagnostic-Code: x-unix; can't create user output file```

server quota was at the default 1gb …ffs it went over the limit without me knowing… but mail was getting blocked… that quota was server settings not quota in the email user settings