Some troubles on Digital Ocean with IPv6
Some of my clients have a several droplets on DO and it’s no wonder that they make use of IPv6, which DO kindly offered. Around two days ago some servers started to fail send an email through an SMTP server on DO.
We have checked everything in an effort to understand what is going on and why email server suddenly stopped its works. It racked the our brains of this cause. The last-ditch bid was to ask DO support. They kindly speak us that IPv6 is experimental and they block Ipv6 for SMTP.
Solution of the problem is disable IPv6 for SMTP. Because a droplet trying to send email by IPv6 at first, then by IPv4, usually it failed by timeout. You might use IP address instead of a domain name or temporary delete AAAA records for your SMTP server in DNS.