sendmail is still a major player as is exim. The business is moving to webmail interfaces as that way you dont have to have phonecalls from people who cannot understand how to setp a mail client.
sendmail is configurable via webmin. (never used it myself bit Imric swears by it) Now are these your webapps or company webapps, scale makes a difference.
Company webapps, the easiest way is to just call an smtp aware program
psuedo code
mailx -s "you lost the password ahole" willieswonka@kermit.frog
password is foobar, its only good once so dont forget to change it
bye
me at bigriver etc
.
end psuedo code
HTH
bill