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.

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 Incoming Emails

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

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


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


cat /etc/mail/local-host-names


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/ > /etc/mail/


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 domain delivered to


2. All emails addressed to will forward to local user jarvis. jarvis


3. All emails addressed to will forward to domain with corresponding usernames.


4. All emails addressed to will be rejected my mail server with acknowledging sender with the message 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 file.



Add entry if not available and compile configuration file

sudo m4 /etc/mail/ > /etc/mail/


Now restart Sendmail service

sudo systemctl restart sendmail


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