The article is modified from Linux Configure Sendmail as SMTP Mail Client ( submission MTA )

In order to configure CentOS sendmail as a submission-only mail client, do follow the steps below. Sendmail can accept and send SMTP email requests from the local server. Outgoing MT always in a queue-only mode.

Configuring Sendmail in Queue-Only Mode

# vim /etc/sysconfig/sendmail

Modify the “DAEMON” line. Set DAEMON=no. This will make sendmail to be executed in a queue-only mode on the machine. The SMTP Server will sent but not receive mail requests.

DAEMON=no

Configure Mail Submission

Configure local server to use central MTA  to be the sender of your mail for your domain

vim /etc/mail/submit.cf

D{MTAHost}mailproxy.myLAN.com

# service sendmail restart

Test Mail

$ mail -s 'Test Message' mymail@mydomain.com < /dev/null