From what I have gathered from just searching the web, Neomail is a Web Based email client. This is very different from a backend mail program called Sendmail. Sendmail is what is know as a Mail transfer agent. It does the hard stuff of actually, finding a route to the host, opening up a connection to the host and delivering it to the host computer. For more on this see:
http://www.sendmail.org/email-explained.html
Neomail, is a webbased email client that is written in Perl. All that it does is provide a nice graphical way to view your mail, by reading the /var/spool/* directories for any new mail. (These directories being run by a email server like postfix or exim or something ). To sendmail, the application most likly actually uses SENDMAIL or something equivalent.
Now if I totally screwed up and neomail is something different... then yes you can change what program sends your mail by editing you php.ini file:
sendmail_path =
point this to whatever your Transfer agent is.
Hope that helps!
