System: Ubuntu 20.04 (LTS) ISPConfig version: 3.2.2 PHP CLI version: 7.4.15 Using postfix and dovecot. Everything is working except incoming email. I can login to roundcube and can send mail, but can't recive it. When I try to send mail from [email protected] (or another mail service) to [email protected] I getting this massage to my gmail. Code: Received: by mydomain.tld (Postfix) id 5204D17B6E0; Wed, 24 Feb 2021 13:41:07 +0000 (UTC) Date: Wed, 24 Feb 2021 13:41:07 +0000 (UTC) From: Mail Delivery System <[email protected]> Subject: Undelivered Mail Returned to Sender To: [email protected] Auto-Submitted: auto-replied MIME-Version: 1.0 Content-Type: multipart/report; report-type=delivery-status; boundary="6253A17B6DD.1614174067/mydomain.tld" Content-Transfer-Encoding: 8bit Message-Id: <[email protected]> --6253A17B6DD.1614174067/mydomain.tld Content-Description: Notification Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit This is the mail system at host mydomain.tld. 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 <[email protected]>: unknown user: "admin" Here's full mail log from /var/log/mail.log (named mail.txt) and short mail log after sending mail from [email protected] to [email protected] (named shortmail.txt).