Looking for good emailing service

I have a couple of clients that send bulk emails to association members. They have both been using internal email servers to handle the work. I am suggesting that they look to an emailing service provider. I envision a service with an ability to maintain the member/email address database remotely, a good attempt at Internet security (don’t want to lose control of the list), decent bandwidth, and an ability to send thousands of emails a day.

This is not spam I’m talking about, either. I hate spam, and am satisfied that I am not helping spammers.

Can you recommend one ?