[LogicX]

We (http://metascribe.com) use mandrill from mailchimp for our inbound mail which appears for now to be free - works great for our purposes. Everyone thinks of them as only outbound and inbound is not a function they highlight, so figured I'd mention it.

http://Mandrill.com

[kawsper]

I think Mandrill is for sending out e-mails, which is quite different from what this post is about.

[LogicX]

Updated patent to emphasize that this is why I'm mentioning it:

They offer an inbound feature which isn't emphasized!

[g8oz]

So does SendGrid.com