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.