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The Basics of Mail Services. As the tome on the send mail e-mail server has over a thousand pages we can just scratch the surface of e-mail services. Common services for e-mail include sendmail in lowercase which is in contrast to its commercial variant, Sendmail uppercase as well as Postfix. These two are essentially outgoing e-mail services, yes there are others but these are the two that are listed in the objectives and these two services are associated with SMTP, short for the Simple Mail Transfer Protocol. In contrast Dovecot can help handle incoming e-mail for both POP3, that's the Post Office Protocol and IMAP4, that's the Internet Message Access Protocol. The noted SMTP services use the etc/aliases file. Take a look at that file in your system; it may have one user or lots of users which forward e-mail from said users to others. Depending on the selected e-mail server, such aliases could even forward emails to regular users. But before that can happen you'll need to run the newaliases command which processes the list from this file into a database that can be used by sendmail, Postfix and even others. When installed sendmail includes its configuration files, primarily in the etc/mail directory. The main sendmail configuration file is sendmail.cf which is a very long file, 2 or 3 thousand lines that can be generated from a macro file. Normally configured as sendmail.mc. That macro file is processed with a make file from the noted directory using the M4 macro processor. In contrast the Postfix server stores configuration files in the etc/Postfix directory, configured in main.cf and master.cf configuration files. Changes to said files are processed normally, by restarting the Postfix Service. Finally the Dovecot configuration file is etc/dovecot.conf it's somewhat simpler in a number of ways. Not only does it support the POP3 and IMAP4 protocols you can see in your version of the file it also supports with the proper configuration the secure version of said protocols which will be listed as POP3S and IMAP4S. Well those are the basics of Linux Mail Services. Thank you and on to the next video.