Cannot send message from Webmail: Temporary lookup failure

Symptoms

• Cannot send an email from Webmail:

  SMTP Error (451): Failed to add recipient "[email protected]" (4.3.0 <[email protected]>: Temporary lookup failure)

• SELinux is enabled:

  # getenforce
  Enforcing

• The following error can be found in
/var/log/maillog:

  server postfix/trivial-rewrite[20662]: warning: hash:/var/spool/postfix/plesk/virtual_domains is unavailable. open database /var/spool/postfix/p
   lesk/virtual_domains.db: Permission denied
   server postfix/smtpd[5590]: NOQUEUE: reject: RCPT from unknown[192.0.2.2]: 451 4.3.0 [email protected]: Temporary lookup failure;
   [email protected] [email protected] proto=ESMTP helo=<[192.0.2.3]>

• Check of SELinux context shows the following:

  # ls -Z /var/spool/postfix/plesk/virtual_domains.db
  -rw-r–r–. root root unconfined_u:object_r:user_tmp_t:s0 /var/spool/postfix/plesk/virtual_domains.db

Cause

Invalid SELinux context.

Resolution

1. Connect to the server via SSH
2. Restore SELinux context for the Postfix files:

   # restorecon -R /var/spool/postfix

Note: In case the issue remains, check that SELinux is configured properly following the resolution from the article below: Unable to send and email: Unable to open file /var/lib/plesk/mail/srs/secret: Permission denied