Yes, I meant non-residential, and also not AWS. The problem with AWS is that a lot of spammers use it, and so a lot of AWS IP addresses get tainted. If you go with a smaller ISP that charges more it's less likely that their clients will be spammers. But to be fair, I've never tried running a mail server on AWS. It's possible that you could do it and not have any problems, I don't actually know. It's probably an experiment worth doing.