Mail not delivered to a mailbox: User unknown in virtual mailbox table

Symptoms

• Mails sent to john.doe@example.com hosted on Plesk server are not delivered and below error can be found in /var/log/maillog:

  CONFIG_TEXT: john.doe@example.com: host mail.example.com[203.0.113.2] said: 550 5.1.1 john.doe@example.com: Recipient address rejected: User unknown in virtual mailbox table (in reply to RCPT TO command)

• Ownership and permissions are different from "popuser popuser  drwxr-x---" for  /var/qmail/mailnames/example.com, for example:

  # ls -lahd /var/qmail/mailnames/example.com/john.doe
  drwxr-xr-x 5 root root 4.0K Jun 27 15:51 john.doe

Cause

Incorrect permissions/ownership for mail folder.

Resolution

1. Connect to the server via SSH

2. Execute below command to set correct permissions and ownership:

   # plesk repair mail example.com -y