Sendmail is a mail transfer agent (MTA) used to route and deliver email over the Internet. Originally developed in the early 1980s, Sendmail was one of the most widely used email routing programs, especially on UNIX and Linux systems. It handles the process of sending email from one server to another, often over the Simple Mail Transfer Protocol (SMTP).
Stable: Sendmail 8.18.2. See Sendmail FTP releases.
MTA Functionality: Sendmail acts as a bridge to move mail from the sender’s system to the recipient’s mail server.
Highly Configurable: It allows complex configurations for routing email, filtering, and supporting multiple domains.
Protocols Supported: It primarily uses SMTP for email delivery but can also support other protocols as needed.
Mail Filtering: Sendmail allows the use of Milter (Mail Filter) to integrate custom email filtering tools for security and anti-spam measures.
Scalability: Suitable for both small and large-scale email systems.
Compatibility: Works well with various UNIX and Linux distributions.
Sendmail’s configuration is generally stored in a file located at /etc/mail/sendmail.cf, though it is not typically edited directly due to its complexity. Instead, the configuration is often generated using a simpler sendmail.mc macro file, which is then processed to produce the sendmail.cf.
sudo apt-get install sendmail on Debian-based systems).sendmail.mc: Modify the sendmail.mc file to suit your needs.sendmail.cf: Use the m4 macro processor to generate the sendmail.cf file from sendmail.mc.m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
sudo systemctl restart sendmail
/var/log/mail.log or /var/log/maillog for Sendmail logs.mailq to view the mail queue and sendmail -q to process the queue.sendmail -bt to test and debug the configuration.