I’ve been running a dual-stacked IPv4/IPv6 email server for a while now on DO, which works fine for inbound mail. However, outbound IPv6 connections to tcp/25 are clearly blocked by DO, which is pretty maddening.
The problem is definitely DO. I have specifically allowed IPv6 outbound to tcp/25 via the host-based iptables/ip6tables/ufw firewall, as well as via DO’s virtual firewall (managed by me from the DO GUI) applied to the droplet where my mailserver lives.
But DO is blocking IPv6 tcp/25 somewhere else that I cannot configure! You can’t even netcat via IPv6 from one DO droplet to another DO droplet on tcp/25.
Yet DO allows tcp/25 outbound via IPv4. That’s just messed up and unless there is a solution very soon I will be looking for another hosting company that doesn’t treat IPv6 as a second-class protocol.
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