The problem with DO and other cloud providers is that it might happen that complete IP subnets are blocked by some providers or are on Spamhaus for example. If

The problem with DO and other cloud providers is that it might happen that complete IP subnets are blocked by some providers or are on Spamhaus for example. If they have been used for spam once before it's super hard to get them "clean" again. This is why I am running my own mail servers on my own IP addresses, because of that I don't have such problems, even sending to the big providers you mentioned is no problem.