How will this be abused?

[Joshua Baer]

How will people abuse the X-Expires header?

Clearly if it made something more important then spammers would have to tradeoff between avoiding the spam folder and getting deleted automatically.

If it just makes things get deleted, then I guess they would only use it if they thought that it reduced spam complaints. But at that point, even though spammers would be using it, it wouldn't really be causing any harm. They would have sent the spam anyway, this just makes it get deleted faster.

What other security concerns are there?

~Josh

[Matt Bowman]

I think that when we first spoke about this we agreed that neither of
us could think of a way to abuse this that is detrimental to the user
experience.

mb

[Joshua Baer]

I think the risks come into play when its implemented in the UI. If expiring messages are highlighted or flagged in some way. Or the Priority Inbox example. If its just being moved to a folder, archived, or deleted then I can't see the risk.

Maybe we could suggest that if all you're doing is moving it, there is no need to authenticate the sender, but if you take other actions you should factor in sender reputation as well.

~Josh

[Krish]

If we allow the expire header to have any expiry - let us say few
minutes - then spammers can potentially get the benefit of the
immediate opens that come from most active users or notifications
(like messenger toasts) and not be dinged by complaints from users who
check mail less frequently. Also, most systems use some kind of a
ratio of delivered mail to complaints as part of their reputation
algorithms and it would be interesting to see what kind of holes this
opens up based on the ratios (complaints to volume), thresholds
(absolute complaints), and sliding windows (over "X" time units).

Might be interesting to see the numbers in practice but it is not
completely out of realm of possibilities if receivers honor this of
the gate only for reputed senders before expanding the offering - just
like what happened with unsub header. The UX concerns are interesting
but can be addressed using the same approach of selectively showing UX
by marrying the header with additional information you have on sender
like their reputation.

~Krish

[M]

Can you alter these emails so they do not expire by policy? Archiving
is important for legal purposes for a number of us. How can how can
you be certain that this cannot be abused to avoid reasonable, legal
surveillance of an employee's behaviour?

[Joshua Baer]

Expiring would be no different than deleting. Archiving systems still
save emails that the user deletes - this would work the same way.

~Josh