Cannot send message from Webmail: Temporary lookup failure

Symptoms

• Cannot send an email from Webmail:

  CONFIG_TEXT: SMTP Error (451): Failed to add recipient "jdoe@example.com" (4.3.0 <jsmith@example.org>: Temporary lookup failure)

• SELinux is enabled:

  # getenforce
  Enforcing

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

  CONFIG_TEXT: 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 jdoe@example.com: Temporary lookup failure;
  from=jdoe@example.com to=jsmith@example.org 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