There are mean people on the internet :(
I've worked at a web hosting company before - not a major operation at a time, but we did enough business to staff one floor of an office building with our support and management people.
Something like 25%-50% of our support volume was spammers and scammers trying to sneak under the radar and get us to restore their service after we'd blacklisted them. A significant portion of these were using stolen credit cards.
Honestly, good luck - but you're going to find that giving away something for free to other people is very different than running it for yourself right about the first time something goes wrong and a few thousand very angry people want to know what's up with their email.
(and as an aside, I really think good email service is worth paying for, and having been woken in the middle of the night to fix things that customers never even noticed - I know that it won't stay surprisingly pleasant forever)