Which Autoreponder Lets Me Import a CSV File with Single Opt-In?

I have a local small retailer as a client. He collected names, email addresses and their birthday month for his customers and now wants to add this information to an autoresponder service and start mailing his list.

The information is in CSV format and he wants to be able to import it into a list service provider with single-opt-in. This information was collected on a sign-up sheet in his store and he really doesn't want to risk losing people because they aren't savvy enough to opt-in when they get an email from him the first time.

Which list service providers will allow this? Imnica is causing me problems, and while I understand their need to be cautious, this is a genuine list and I need to find a solution which doesn't cost an arm and a leg for a real-world business just starting out in the virtual world.

My client expects to continue to add sign-ups at his store and so he will also need a way to manually add 10-20 sign-ups from time to time without triggering a problem if they all come from the same IP address.

Any leads to the right service providers gratefully received.



Thanks,

Debbie