Ummm, actually sendmail as such has very little to do with it. Since SMTP is a socket-based mail delivery protocol, he needs a socket service, either locally or remotely, that Net::SMTP can connect to, to provide SMTP service.
To this end, MS Exchange, or several freeware clients can provide this service. Having sendmail is only relevant to programs that are trying to exec sendmail to send mail (and that's really an obsolete way to do it, these days).
Someone mentioned Blat
in a previous post. Blat does not provide SMTP service as socket provider, but will connect to a SMTP server and send the mail provided on the command line or parameters file. Several years ago I had written a Windows App that needed Blat to send mail, since there were no SMTP class libraries available. And you really don't want to write your own, since a number of the SMTP servers out there are somewhat quirky.