Transactional emails not delivered if the account’s owner has changed in the meantime.
When in June,
Yahoo
announced
it would free up inactive user IDs, it received fierce criticism from the security community.
The concern was that many of these user IDs are tied to email addresses that, though dormant, may still be registered as the back-up address to other online accounts. Access to such a
Yahoo!
account could thus allow someone to take over the original owner’s
Gmail
or
Facebook
accounts.
Yesterday,
Yahoo!
started to
release
some of the recycled user IDs. However, to mitigate the damage, it is accepting a
new email header
that senders can use to tell
Yahoo!
when the address was last confirmed.
If, for instance,
Faceook
sends a password reset to a
Yahoo!
email address, it includes a
Require-Recipient-Valid-Since
header, indicating when the address was last confirmed.
Yahoo!
will only deliver the email if the owner of the address hasn’t changed since that time.
The header is the subject of a
draft
currently under review at the IETF.
I think this header is a really nice idea. The reissuing of email addresses was a problem before
Yahoo!
started doing so on a large scale: several ISPs are known to reissue addresses of former customers and in many organisations it is common practice for a new employee to receive email addressed to their predecessor.
I would certainly hope that many senders of transactional email would start using this header. At the same time, I would also hope its use would be constrained to these emails: I don’t think it would be desirable if email marketers simply added this header to their emails rather than unsubscribing users whose emails bounce.
However, while I understand
Yahoo!
‘s reasons for freeing up inactive user IDs, I’m still not convinced they’ve done enough to prevent possible damage. At the very least they should have waited until the draft had been accepted by the IETF and the practice of using the headers had been more widely adopted by senders of transactional email.
From a security point of view, I’d still rather have seen that
Yahoo!
didn’t touch these old user IDs, no matter how dormant they may have been. A better alternative would have been to purchase a new domain name and use this for new customers not happy with the
[email protected]
address
Yahoo!
could offer them. But, once widely implemented, this new header could make the problem a lot less serious.
Posted on 27 August 2013 by
Martijn Grooten
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