What does the following warning found in the
postfix/smtpd: warning: dict_nis_init: NIS domain name not set - NIS lookups disabled
The NIS (Network Information System) allows "a group of machines within an NIS domain to share a common set of configuration files." If there are email servers running on more than one box, NIS can share the configuration files between them.
This warning may be safely ignored as it does not cause problems when there is a single server running.
Apply these steps to remove the warning:
Connect to the server via SSH.
Run the following command to get the "NIS" line from the Postfix configuration utility:
# postconf | grep "nis:mail.aliases"
alias_maps = hash:/etc/aliases, nis:mail.aliases, hash:/var/spool/postfix/plesk/aliases
Remove the "nis:mail.aliases" fragment from postfix configuration file by running the following command:
# postconf -e "alias_maps = hash:/etc/aliases, hash:/var/spool/postfix/plesk/aliases"
Restart Postfix service to apply the changes:
Warning: restarting Postfix would cause some downtime for mail delivery, perform the restart during a maintenance window
# service postfix restart