The main configuration file of sendmail is /etc/mail/sendmail.cf, however adjusting that is not part of this tutorial. If you want to adjust the configuration files of sendmail, you can usually find them in the directory /etc/mail/ on UNIX (FreeBSD, OpenBSD) and Linux (CentOS, Fedora, Debian, Ubuntu) systems. The above output means that the full path to our sendmail command's binary file is /usr/sbin/sendmail which you should note for the steps further below. To figure that out, we'll use the which command as shown below: ~]# which sendmail The first interesting information that we might need for testing sendmail is the path of the binary file that gets executed if we issue the command sendmail on our command line. Where Is Sendmail And Its Configuration Files Located? Like the name already suggests, sendmail itself can only send emails and not store received ones in POP or IMAP mailboxes. Using the sendmail command might be the most easy way to send e-mails via Linux shell CLI (Command Line Interface), apart from mailx, which can be used in conjunction with sendmail to make it even easier to send and receive mails from command line. While there is a commercial version available which is called "Sendmail", the sendmail we're covering in this how-to article is the UNIX-based version of it, which comes with pretty much every Linux distribution as well as *BSD (FreeBSD, OpenBSD and variants). Sendmail is a very plain and simple MTA (Mail Transfer Agent), which implements the SMTP (Simple Mail Transfer Protocol) amongst others and can be used to transmit emails, typically even on the cheapest KVM VPS running Linux.
How to Test Sendmail From Command Line on Linux