Weird naming `NewSMTPClient`

[IceflowRE]

NewSMTPClient should be NewSMTPServer or at least it should be documented, why this is how it is.

[xhit]

I confirm a mistake with names. Also see #37

I will document this in next days.

[Foosec]

If i could add, its not just the use of the "server" variable,
a function called NewSMTPClient returns a SMTPServer
Perhaps the function should be changed to NewSMTPServer, although i understand the predicament with that aswell.

Maybe NewSMTPEndpoint?

Just my 2c

[xhit]

It's time to V3 so make all your ideas here: #53