How to Install Sendmail on Debian 9 (Stretch)

Sendmail is a MTA (Mail Transfer Agent) server used for transferring email from between different hosts. Sendmail uses SMTP (Simple Mail Transfer Protocol) protocol. Most of the system administrators preferred to use Sendmail server as MTA than other MTAs. This tutorial helps you to Install Sendmail on Debian 9 (Stretch) Linux system.

1. Install Sendmail

If you don’t have installed Sendmail using the following command to install Sendmail with other required packages using the apt package manager.

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sudo apt update
sudo apt install sendmail sendmail-cf m4

2. Configure Sendmail Server

Now, execute the sendmailconfig command to complete the basic configuration.

sudo sendmailconfig

Select all options to ‘Y’ and press enter. Wait for the command finish.

Your server is ready for sending emails. You can use the Linux command line or PHP script to send emails.

3. Receive Incomming Emails

Edit /etc/mail/sendmail.mc file and comment below line to allow receiving an email from anywhere. To comment a line in sendmail.mc, just put dnl keyword at the start of the line.

dnl DAEMON_OPTIONS(`Family=inet,  Name=MTA-v4, Port=smtp, Addr=127.0.0.1')dnl
dnl DAEMON_OPTIONS(`Family=inet,  Name=MSP-v4, Port=submission, M=Ea, Addr=127.0.0.1')dnl

Then add your domain names to /etc/mail/local-host-names file.

cat /etc/mail/local-host-names

tecadmin.net
mail.tecadmin.net
localhost
localhost.localdomain

Now use m4 is a macro processor to compile the Sendmail configuration files. m4 is stream-based, that is, it doesn’t understand about lines.

sudo m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

Restart Sendmail service

sudo systemctl restart sendmail

Your system is ready for incoming emails.

4. Configure Domain-based E-mail Routing

As we read above that virtusertable file used for aliasing, allowing multiple virtual domains to be hosted on one machine.

• 1. All emails addressed to @example.com domain delivered to [email protected]

  @example.com [email protected]
  

• 2. All emails addressed to [email protected] will forward to local user jack.

  [email protected]  jack
  

• 3. All emails addressed to @mydomain.com will forward to domain @otherdomain.com with corresponding usernames.

  @mydomain.com    %[email protected]
  

• 4. All emails addressed to @otherdomain.com will be rejected my mail server with acknowledging sender with the message

  @otherdomain.com 	 error:nouser User unknown
  

After making all changes in virtusertable execute the following command to create an updated virtusertable.db file containing the new configuration.

sudo makemap hash /etc/mail/virtusertable < /etc/mail/virtusertable

Also make sure the following entry is added in sendmail.mc file.

FEATURE(`virtusertable')

Add entry if not available and compile configuration file

sudo m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

Now restart Sendmail service

sudo systemctl restart sendmail

Thanks for reading this article. I hope this article will help you to configure Sendmail on Debian 9 (Stretch) system.

References:
http://www.sendmail.com/
http://www.sendmail.com/sm/open_source/docs/m4/intro_m4.html