Re: History of fallback to A
Russ Allbery writes:
For example, here at Stanford, there are a ton of departmental servers
that accept mail for some reason, and almost none of them have MX
records. People only add MX records when they need to direct mail
addressed to one system to a different one instead.
There are three cases:
1. The operators of such a server never add an AAAA. Nothing changes. MX
lookups still fall back to A.
2. The operators of such a server add an AAAA at some point. IMO, adding
MX at the same time is sound practice, but it's not strictly necessary,
because there is an A and MX lookups still fall back to it.
3. The operators of such a server adds an AAAA and removes the A, or
cannot get an A. In this case, an MX really has to be added.
Is this onerous?