We recently discovered that DigitalOcean is blocking some outgoing IPv6 ports - more specifically, in our case those were outgoing email ports: 25, 465, 587 (emphasis on outgoing, not incoming ports).
You can test this by entering following command to your DigitalOcean console:
telnet -6 smtp.gmail.com 587
This is quite a limitation for us since we can not monitor email servers for our customers on IPv6 addresses. Fortunately our monitoring solution is very flexible so we can simply flag DigitalOcean monitoring agents as "not IPv6 capable" so they are not used for IPv6 monitoring at all.
We don't know if they block more ports because we can't find any documentation for this. With this post we wanted to inform you about this limitation so you can consider other VPS providers if you need unrestricted outgoing IPv6 connectivity. Vultr and AWS for example do not have such limitations.