sending mails in an intranet

Hello,

I setup an intranet site with wp and send mails with mandrill on it.
Ever since the mail chimp, mandrill integration ive been unable to connect accounts and its just becoming a whole complicated process.
Ive tried sendgrid but they require that i verify my domain but cant do that since its on an intanet.

Does anyone know anyway i can go about this with any other sending mail api service and how to go about it?