This Growl plugin was developed in 2011, back when Growl's email capabilities were rather basic. MailMeToo was built to replace the MailMe notification style for those who weren't happy with it. Instead of routing notifications through Mail.app, MailMeToo connects to a specified SMTP server and directly sends the notification as an email message. The original release name was SMTP Mail.
With Growl 2.0, MailMeToo was pulled into Growl to replace the original MailMe plugin. For that reason, you don't need to install this plugin anymore, unless for some reason you're using an older version of Growl (specifically, version 1.2.2).
This project contains an Obj-C implementation of the SMTP protocol.