On 30 May 2013, at 14:30, Jay Ashworth wrote:

I just subscribed to the virtualgl-users list at SF, and I subscribed with
a plushacked email address, jra+vgl@

Got the confirmation email ok, of course, but when I tried to send something, it bounced "because I'm not subscribed to the list". I've never had that happen before, but it's possible that I've never tried to sub a plushack
address to a Mailman list.

Does Mailman in fact not understand plushacked addresses as subscription
addresses, and that it should canonicalize them when a) checking for
duplicate subscriptions and b) accepting messages for restricted lists?

It is altogether always wrong for ANY mail software outside of a domain to parse the local part of an address in that domain except for a tiny handful of standard special local parts (e.g. "postmaster"). The use of '+' as a tag delimiter is widespread but it is not in any sense a "standard" and comes nowhere near universality. There is no way for a Mailman instance to know which domains make "user+tag" and "user" equivalent and which do not, so canonicalizing as you suggest would result in breakage.

Beyond that risk of breakage, "canonicalizing" local parts which one does not own is wrong in principle: it violates the core assumption which makes Sendmail-style plus-tagging useful. The tagged address is supposed to be unique in the view of everyone except its owner and the owner's delivery agent, which can easily discern that an address is tagged (maybe with '+' but maybe not) and then handle the address and tag in whatever locally customized manner their whims dictate. Outside entities should never try to guess what those whims are at any particular time and more importantly should never translate an address from what it actually is to what their guesses about the owner's whims implies.

Note: you might look at my address for this list and make any of a number of reasonable guesses about how its structure (which *IS* significant) relates to its delivery and handling. Most would be operationally wrong and none would be complete. I tag addresses in opaque ways precisely because of past rude & clueless attempts by others (mostly spammers) to break + tagging.

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