Linux Configure Sendmail as SMTP Mail Client ( submission MTA )

I've central e-mail server. Other servers does not need to operate as a mail server. How do I configure Sendmail as submission-only e-mail server (mail client) under CentOS / Fedora / RHEL / Debian Linux / UNIX like operating systems?

Sendmail or any MTA can work in two different modes. It can accept incoming SMTP e-mail requests and send mail from the local machine / workstation or server (cluster node). This is called outbound MTA and it always runes in a queue-only mode.

Step # 1: Disable Sendmail Daemon In a Listing Mode

Edit the file /etc/sysconfig/sendmail using the text editor such as vi, enter:
# vi /etc/sysconfig/sendmail
Modify the line:

DAEMON=no

Save and close the file. Setting DAEMON=no tells Sendmail to execute only the queue runner on this machine, and never to receive SMTP mail requests on port # 25.

Step #2: Configure Mail Submission

You need to tell sedmail about a central MTA which will accept mail on port # 25 for all your domains. For e.g. mail.nixcraft.net act as a central MTA. Edit /etc/mail/submit.cf, enter:
# vi /etc/mail/submit.cf
Find the line beginning with D{MTAHost}, and update it to read as follows:

D{MTAHost}mail.nixcraft.net

Save and close the file. mail.nixcraft.net is the hostname of the server to which this machine should forward its all outgoing mail. Please note that mail.nixcraft.net must be configured to accept mail from your other workstations or server. Once done reload sendmail.

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