On Fri 02/Jun/2023 02:14:50 +0200 Brandon Long via mailop wrote:
On Thu, Jun 1, 2023 at 11:20 AM Alessandro Vesely via mailop.org wrote:
On Thu 01/Jun/2023 17:45:38 +0200 Robert L Mathews wrote:
So I guess it's time to add SRS rewriting for Gmail addresses...!
The only points I see in SRS are mailbox full or oversize. [...] But this
does not happen so frequently any more. [...] Permanent failures, 5xx,
are permanent, like cancelled account. In that case, SRS doesn't do a
good job. It is better to remove the forwarding instructions completely,
no?
I feel like SRS is trying to be something more than just VERP, but the more
was never really flushed out.
The "more" is validation that you generated the address, so you can ignore
mail that isn't actually a bounce... perhaps if it starts getting spam or whatever.
The issue is that bounces may occur after days, so you would need to make
your address usable for days. And you might get transient bounce messages
("still trying"), or the next hop may not rewrite and forward to multiple
addresses...
Also, sometimes the recipient wants everybody to know about the new address and
possibly take note, but some other times a recipient changed address in order
to cut some contacts, and wants to keep the new address secret. Bounce
handling should differ in such cases.
Anyways, most folks seem to be fine with just a less validated approach, up
to them.
Gmail's forwarding has always used a VERPs like approach with the +=caf
semantics, and yes, repeated bounces of certain types can lead to the
forwarding being disabled... though, there's obviously issues with stopping
forwarding because customers may never be checking the forwarding account. >
Also, 5xx means permanent failure just for that transaction, not for the
account ever... though one can try and deduce whether the latter is true.
5xx implies human (or at least out-of-band) intervention. The question is
which human, the recipient, the sender or the sysadmin? Any numbers on the
frequencies that these occur, anyone?
Behavior is presumably different if there are other means to contact the
recipient...
Anyways, obviously folks who forward should not respond to the sending
server until the message has been accepted by the forwarding server, and any
smtp rejection should be propagated directly to the sender... oh, and spam
check before even attempting to forward, of course.
Some systems automatically switch to reject after the first delivery failure,
as an anti-backscatter mechanism. To do the same with forwarding failures one
has to remove the dot-forward. That might be considered parallel to mailing
lists auto-unsubscribing after a few rejections.
Best
Ale
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