Everytime Plesk installs updates users can't sent any e-mail after each update.
When a user tries to send an e-mail, the logfile shows:
Aug 6 07:10:06 server postfix/smtp[25791]: DB8D324D1D: to=<
[email protected]>, relay=none, delay=0.22, delays=0.16/0.06/0/0, dsn=4.4.3, status=deferred (Host...