These configurations are based upon my own experience, and the
experience of others.  Careful installation of any of these
configurations will result in a solid, reliable mail system
that respects the appropriate "do's and don'ts".  Each configuration
represents a compromise of ease of installation and maintenance
versus sophistication and capabilities.

One thing you should consider is what you already have on your
system.  You will invariably have "binmail", and will have a good
chance at already having sendmail.  Some systems come with
smail (if 2.3, junk it)  The configurations shown below are *minimal*
configurations, so you should consider whether you want to use what
you already have or not.

Scenario 1:  Only UUCP connections.

    Smail 2.5.  If you want to set up a routing database of
    your own, you will also need pathalias, and unpackmaps or
    uuhosts.  Instead, though, you can configure smail 2.5 to
    smart-host most destinations to a nearby friendly site
    who'll do your routing for you without having to run
    the routing software.  Note further, that you can run
    pathalias on just a subset of the full set of maps.
    [Unpackmaps makes this particularly easy to do]

    Smail 2.5, as shipped, does not support mail-to-pipeline
    or mail-to-file aliasing.  If you need these, at a minimum,
    you should obtain lmail.  If you intend more than casual
    use of these features, it is recommended that you obtain
    deliver or procmail instead of lmail.

    Even if you have sendmail already, you can integrate smail 2.5
    with it to do your UUCP routing.  (though, some later versions
    of sendmail can do routing themselves)

    If you're a little more demanding of your mail connections, smail 3
    is also a good choice, and works particularly well for systems that
    are UUCP connected to Internet sites.

Scenario 2:  SMTP connections (optionally, some UUCP connections too).

    Generally speaking, sendmail will do this for you and you have
    a good chance to have it already.  However, for the novice, it
    is recommended that smail 3 be used instead [see review of
    sendmail below].  Smail 3 includes all of the routing software
    and can do mail-to-pipeline and mail-to-file, so none of the auxiliary
    programs mentioned in scenario 1 are necessary.

    Most sendmails don't include UUCP routing mechanisms, so you would
    need pathalias and unpackmaps or uuhosts if you wish to set up
    a UUCP routing database.  Further, most sendmails don't know
    how to query a pathalias database directly, so you may have to hack
    your own path lookup program into the sendmail.cf (smail 2.5 can
    be used for this purpose provided that you will have a UUCP link
    to the outside world)

    Both MMDF and PP can also be used, but PP is usually overkill.

    Deliver or procmail are still quite useful in this configuration
    for extended alias facilities.

Scenario 3:  Connections to other networks (optionally including
    SMTP or UUCP), or very high loading.

    Your best bets are MMDF, PP or zmailer.
    
    You can implement other network interfaces with sendmail, but
    not only will you probably have to roll your own, but sendmail
    can't cope with high loading very well.  Ditto smail 3.

There are other configurations.  See the Package Reviews to
determine which packages are appropriate.