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/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 support@mydomain.com
@example.com support@mydomain.com
2. All emails addressed to support@mydomain.com will forward to local user jarvis.
support@mydomain.com jarvis
3. All emails addressed to @mydomain.com will forward to domain @otherdomain.com with corresponding usernames.
@mydomain.com %1@otherdomain.com
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
