Email Marketing Management

Hey everyone! Been reading for a while, but this is my first time posting. Hello!

My customer and affiliate mailing lists are getting to large to manage by hand.

Can anyone recommend a good company for email list management and newsletter delivery? Something like ConstantContact or iContact but that allows adult content?

Or are newsletters dead and I should publish an RSS feed to provide info to customers/affiliates about updates instead?

How do affiliates prefer to receive info from sponsors? Email? RSS? Other?

Thanks guys.

I've used DadaMail for years. It's a sound solution from my experience.