2.2 Configure sendmail Service for Local-Only Mode


In Solaris 11, the sendmail service is set to local only mode by default. This means that users on remote systems cannot connect to the sendmail service, eliminating the possibility of a remote exploit attack against some future sendmail vulnerability. Leaving sendmail in local-only mode permits mail to be sent out from the local system. If the local system will not be processing or sending any mail, this service can be disabled.
However, if sendmail is disabled completely, email messages sent to the root account (such as cron job output or audit service warnings) will fail to be delivered.
An alternative approach is to disable the sendmail service and create a cron job to process all mail that is queued on the local system, sending it to a relay host defined in the sendmail.cf file. It is recommended that sendmail be left in local-only mode unless there is a specific requirement to completely disable it.

The software for all Mail Transfer Agents is complex and most have a long history of security issues. While it is important to ensure that the system can process local mail messages, it is not necessary to have the MTA's daemon listening on a port unless the server is intended to be a mail server that receives and processes mail from other systems.


Run the following to set sendmail to listen only local interfaces:
# svccfg -v -s svc:/network/smtp:sendmail setprop config/local_only=true
# svcadm refresh sendmail
# svcadm restart sendmail

See Also