unavoidable in that case. I don't know how widespread this usage of
mail sent (not received) with domain parts that map onto wildcard
MXes with arbitrary subdomains is. I suspect it doesn't actually happen.
Sure it does:
I agree that it's more common to invent per-correspondent addresses to
subscribe to mailing lists, but then to get your message posted, or to
adjust your mailing list settings, you do have to be able to send mail
from that address.
All of the funky things that people do with tagged subaddresses map
directly onto subdomains set up like Panix's (user-tag(_at_)foo ->
tag(_at_)user(_dot_)foo) and I suspect we'll be seeing more of them rather than
less in the future.
I think I still see a certain amount of mail from places that let you
use a workstation cluster and put the workstation name into the return
address. I suppose that the number of workstations in a cluster is
unlikely to be so large as to make the corresponding DNS zone
unwieldy, but up to now you could set up your wildcards appropriately
so you just plug in a new workstation and the mail works.
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