Right now DO blocking is only sparsely documented (some forum threads, https://digitalocean.uservoice.com/forums/136585-digitalocean/suggestions/7190053-allow-smtp-over-ipv6, ... or user's own blog posts).

This causes long debugging runs when trying to figure out why SMTP does not work by default... Until one starts thinking that Digital Ocean itself is the blocker and finds the blog posts :(

DigitalOcean should clearly document blocking choices: the service is otherwise very good and upfront, this really is a sore spot.

I propose we get the warning in the Droplet's networking page.