* Johann Atma could not reach out for any request on the apps forum as register verification mails would not arrive at Atma email account to get access.
It seems that the registration e-mail is rejected from the sangham mail server for similar reasons that
sangham mail was rejected from another server before, when sending via IPv6.
IPv6 is usually only used between mail servers if both support the protocol. If either of them cannot use IPv6, they will use IPv4 (if both have IPv4 addresses).
Some checks are done by the sangham mail server to prove the incoming mail is authentic. But the sending server has not set up its authenticity proof mechanisms right for the case of sending via IPv6. So the check fails and the mail is rejected.
So this would actually count as a configuration problem of the sending mail server here (as it was before a configuration problem of the sangham mail server when sending
in this case ).
The sangham server is simply configured to reject such incoming mail which cannot be properly verified as authentic by these standard mechanisms. This common practice seems necessary to avoid greater floods of spam.
IPv6, even though many years old, is still not very commonly used today, even though its use is increasing. Many servers and mail systems in the world are still not set up correctly (just like sangham.net was not set up correctly until few days ago) to use it. So this problem could happen more often unknowingly.
There are three general solutions I am thinking of now:
1. Disable IPv6 completely on the Sangham mail server, so that all mail could only be sent and received via IPv4. Most e-mail servers have IPv4 addresses and can send and receive via IPv4. It would be very rare still to find an IPv6 only mail server in common use.
They would then not try and fail via IPv6 to send mail to sangham.net, and be rejected when not authenticated correctly.
2. Disable certain authenticity verification checks in case of incoming mail using IPv6. But this would probably invite a lot of spam.
3. Just disable these authenticity checks in some cases, for some known incoming addresses, like the case just noticed here. But it would be difficult to notice such cases usually and all put them on an "allowed" list.
I think 1. would be the easiest and most safe to do.
I will try to do it soon and hope it will not disrupt e-mail service.