I really don't know... I have about 8000 members as of now - I would probably email them about 3-4 times per week with some updates/offers. I haven't got any spam complaints so far (I've been running this service for 3 years now) but if anyone decides they "didn't subscribe" I don't want my server shut just because some idiot doesn't remember he or she DID subscribe.
Most the 'budget' deals located on this site (in the offers section) aren't going to be very tollerant of email complaints (valid or not) - so bare that in mind. But you could check the offers section here at least and ask.
But mostly, anyone generating lots of email complaints is going to get the boot on a sub $200/month server. Generally speaking you will need a double-opt-in mail list (you said opt-in, but not double opt-in your post) to keep the complaints well under the limits. You are correct, people will forget they subscribed and click the 'spam' button on their inbox to file a complaint. Using the double-opt-in list reduces that considerably from the 'single opt-in' check box that most sites sneak in the corner when they signup for a product/service or more information.
What software do you run, or plan to install? I.e. is it a php based script that is compatible with any version of linux with a MySQL database back end? or is it something more specific, or are you looking for a 'managed' provider to provide this and help you (not likely at the sub $200/month level).
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