Installation of ArchiveSMTP should be as simple as:

./configure
make install

However configuring your MTA to use it varies and you will need to consult the
documention for how to use a milter with your MTA. For sendmail you can look at
http://www.milter.org.

Should you have problems it is likely due to missing libmilter. While a number
of MTAs support libmilter they may not come with it or your system may not have
installed it by default.

To get a version of libmilter you can download a recent version of the sendmail
sources from http://www.sendmail.org and unpackage it. Enter the libmilter dir
of the package (usually something like sendmail-x.x.x/libmilter/) and type 'make
install'. If you have problems with this stage you will need to consult the
sendmail website/documentation, but in most cases it should be fairly painless.

An example rc startup script is included which you will need to edit for your
system and place in the correct spot to allow start up on booting, called 
rc.archivesmtp.
