When you say 'reputable' IP do you mean non-residential or is something like AWS, Linode, etc enough?
Edit: duplicate to sibling, apparently I had this tab open longer than I thought.
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.
... can you expand on what you mean by “commercial” hosting?
Sorry, that was a very poor choice of words. What I actually meant was "a small commercial hosting company", i.e. not Amazon. Amazon IPs can have a dicey provenance.
(Actually, the company was recently acquired so they may not be so small any more. The company is called ZeroLag and they were acquired by Total Server Solutions.)
AMA if you decide to take this on, I'm happy to help.