I enabled the watchdog email, now I get a lot of messages containing this:
SMTP WARNING - Invalid response ‘550 5.1.1 <watchdog@localhost>: Recipient address rejected: User unknown in virtual mailbox table’ to command ‘RCPT TO:watchdog@localhost’
CRITICAL - Socket timeout
SMTP OK - 0.051 sec. response time|time=0.050685s;;;0.000000
SMTP WARNING - Invalid response ‘550 5.1.1 <watchdog@localhost>: Recipient address rejected: User unknown in virtual mailbox table’ to command ‘RCPT TO:watchdog@localhost’
CRITICAL - Socket timeout