I'm doubtful a default block would work, as that would even penalise the 'big boys' of email when they make basic network changes and piss off existing customers of both sender and receiver... Its easier and logical to conclude something without reputation yet is therefore sending too few mails to be useful to a spammer.

I've had good experiences with smaller ISPs (currently Mythic Beasts). In contrast, OVH was a poor experience.

I find that reputation (beyond the known "block-lists") appears more likely being tracked for the whole AS number, therefore a lot more to do with your "neighbours" than anything else.

What matters most is if the IP address they issue you has been blacklisted for spamming. DigitalOcean is fine but you need to check the IP address before you do the work of building a mail server. Some of their IPs are on a lot of blacklists.

If it's only on a very few you need to look into who's blacklisting it. There are some that offer a way to get delisted and make it easy, there are others that block pretty much every IP address DigitalOcean has (or large ranges of them) and they won't de-list anything within them. Many of those blacklists are managed overseas and not used much in the U.S.

No matter the ISP you should check the IP address they issue for a VPS before you build the email server.