Mail does not work: milter-reject: END-OF-MESSAGE from localhost.localdomain[::1]: 4.7.1 Service unavailable – try again later

Symptoms

• Impossible to send or receive emails, including between local domains on a Plesk for Linux server.

• Records like the following can be found in the log file /var/log/maillog:

  postfix/cleanup[11217]: 79BBA21A00DD: milter-reject: END-OF-MESSAGE from localhost.localdomain[::1]: 4.7.1 Service unavailable - try again later; [email protected] [email protected] proto=ESMTP helo=<example.com>
  postfix/smtpd[11272]: disconnect from localhost.localdomain[::1] ehlo=1 auth=1 mail=1 rcpt=1 data=0/1 rset=1 quit=1 commands=6/7
  /usr/lib/plesk-9.0/psa-pc-remote[9037]: Message aborted.
  /usr/lib/plesk-9.0/psa-pc-remote[9037]: Message aborted.
  spamd[17708]: prefork: child states: BI

• The extension Warden Anti-spam and Virus Protection is installed on the server.

• Anti-Spam-milter and Anti-Virus-milter are shown as running in the menu  Extensions > My Extenshions > Warden Anti-spam and Virus Protection:
  

Cause

Warden Anti-spam and Virus Protection extension external issue.

Resolution

1. Log into Plesk.
2. Go to Extensions > My Extensions > Warden Anti-spam and Virus Protection.
3. Disable Anti-Spam-milter and Anti-Virus-milter.
4. Contact the extension technical support for the assistance.