IIRC though DO tries to make sure a released IP is returned back to you if you re-provision quickly, you run the risk of losing your well groomed IP for outbound mail if there is an issue with your droplet.

Additionally, IIRC they forbid outbound SMTP on their Floating IP system. (I can't find an official doc on this matter). Either way, you can't get a PTR for your floating IP, which can harm deliverability[1]

For that reason, you may want to consider AWS & an Elastic IP that you can own, groom, and move around [2]

[1] https://ideas.digitalocean.com/ideas/DO-I-1023

[2] https://aws.amazon.com/premiumsupport/knowledge-center/ec2-p...