last i checked (about half a year ago), they didn’t support IPv6. a tired meme, but it actually has economic impacts on my self-hoster friends. almost all ISPs block the SMTP port, and it’s way cheaper (free, even) to get an unblocked IPv6 address than an IPv4 one just because of address exhaustion. so if i used Zoho i’d kinda be forcing them to pay more if they want to be able to reach me :/
I think the idea is that he has friends with SMTP outbound that is only capable of ipv6. Zoho doesn't listen on any ipv6 addresses, and doesn't have any MX records that map to AAAA/ipv6, so mail from them doesn't get to Zoho.
Though I suspect Zoho is not the only medium sized email provider that doesn't support ipv6.
I am Barath and I am a lead customer satisfaction engineer from Zoho Mail team.
We have been working on supporting IPv6 for a while now and are in the final stages of rollout. We will start supporting IPv6 for incoming email reception by this month, This will be rolled out in a phased manner and will be supported for all the accounts by the end of 2022.
Similarly for outgoing email relay, we expect the IPv6 support to be rolled out by the end of Q1 2023.
