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Re: Intent to revive "expires" header fromdraft-ietf-mailext-new-fields-15

2008-07-29 20:51:22

Russ Allbery wrote:

However, I don't think that difference poses any real difficulties for the
definition of Expires.  Regardless of the expectation around when the
message goes away, the existing netnews definition of the field is "this
message will no longer be useful after this date, and you therefore may
want to discard it."  This meaning is just as reasonable in e-mail as it
is in netnews.  (In netnews, it also carries the additional meaning of
"this message will be useful up until this date, so you might want to keep
it for that long rather than discarding it earlier," which it will not
have in e-mail due to different assumptions, but I don't think that's an

In both cases, the effect of the header is entirely advisory and is
determined by the local policy of the recipient, not the sender.

yes, it's advisory in theory. but in practice Expires in netnews means "delete the message on or before this date" for very close to 100% of the servers out there - precisely because in netnews the assumption is that all messages will expire after a relatively short time anyway.

by contrast with email, expiration is relatively uncommon, and when expiration is employed the default timeouts tend to be very much longer.

> The proposed meaning for e-mail and the established meaning for
> netnews are so similar that the only differences I see are
> edge-case quibbling.  I think it would be very strange to use
> a different name for the header in e-mail when basically the
> same meaning is intended.

the definitions as stated are very similar, but the definitions have to be evaluated within their usage contexts - and the two contexts are very different. basically the two contexts are so different that to use Expires in email would likely result in confusing, surprising, and undesirable behavior in email.


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