How to send mails?

[hardballking]

The SendMail() command doesn't work within my addon. Is there any kinde of parameter I have to pay attantion? or are there any special conditons that have to be meet.
EVENT_MANAGER:RegisterForEvent(self.name, EVENT_ACTIVITY_FINDER_ACTIVITY_COMPLETE,self.ActivityEnd)


function TestAddOn.ActivityEnd()
SendMail("@someon", "Titel", text_to_send)
end

text_to_send is just some text