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I considered only the skin-deep workings of email, because configuring sendmail requires a book of its own. More detailed sendmail configuration information can be found in the documentation supplied with the operating system located in the /usr/share/sendmail-cf directory. Also, running a search for "configuring sendmail" in any Internet search system will produce a huge list of hits on this subject.
If this is still not enough, you can buy a book on the subject, for example, Sendmail by Bryan Costales and Eric Allman, published by O'Reilly Media.
If you are just beginning to work with the sendmail service, I recommend that you start with the default configuration settings and proceed from there.