Linux Configure Sendmail as SMTP Mail Client ( submission MTA )

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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.


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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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Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin, DevOps engineer, and a trainer for the Linux operating system/Unix shell scripting. Get the latest tutorials on SysAdmin, Linux/Unix and open source topics via RSS/XML feed or weekly email newsletter.

16 comment

  1. I’m using my own sendmail server like cyberciti.biz as MTA(outbound) and if I need to relay mails of host cyberciti2.biz what settings need to be adjusted in cyberciti.biz host ?

  3. Hi vivek,
    will this work for
    -SMTP authenticated mail servers as well
    -SSL/TLS supported mail servers
    -Mail servers not running on port 25.

    The server in question is google hosted mail server. Can you give any links which details how to point local sendmail to our gmail server to send outbound mails.

  6. Thanks man!!! Awesome tip..Exactly I was looking for..I only needed to option two make it a mail client use a remote server as the outgoing mail server..Thanks a lot!!!

  13. Great but now all the local mail such as root@localhost is heading out to that server as well, need a way to keep the localhost mail on the local server.

  14. Hello, and thank you for this interesting article.
    I wanted to follow those indications, but unfortunately, when running on Fedora 19 release, the sendmail version has been updated to 8.14.7-1, and the content of the /etc/sysconfig/sendmail has been modified.
    the option : DAEMON = no doesn’t seem to exist anymore, and I would like to keep this parameter with the current version of sendmail.
    Do you know where i could have the same option in 8.14.7-1 ?
    I can’t find anything on the internet referring to this :/

  15. Neither this is working for me , i followed above instructions but all in vein.brought up with the below error after sending mail using “mail abc@xyz.com”
    –
    /home/abc_user/dead.letter… Saved message in /home/abc_user/dead.letter

  16. When I send mail from my smtp server to a user, the original message received by that user
    contains my ip address logged in the header. How do I change or remove that ip address?
    Please reply ASAP.

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