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A mail header field to specify action deadlines

While drafting emails to be sent out as part of my research, I just had an idea about a new mail header field, let's call it X-Respond-By. This header field allows the sender to specify when s/he requests/requires/needs a response. The recipient could make use of this in multiple ways:

Obviously, care would have to be taken to prevent abuse, e.g. by some senders who make all their messages require responses on the next day. One way to achieve this would be to give the recipient sender-specific policies to ignore the field, extend it by a fixed period, or simply reject messages with the field set.

I already use a tickler system (which works locally as well as remotely) inspired by the GTD concept of a tickler file, which allows me to have email messages delayed to a given point in the future. I could very well imagine how such an approach could extend into a cooperative communication method.

I am looking forward to your comments.

Update: Jan Hudec wrote in to tell me about the Reply-By field used by Outlook, which sends messages with those headers:

X-Message-Flag: Follow up
Reply-By: Wed, 10 Sep 2008 12:00:00 +0200

According to Jan, this will

will mark the message with specific symbol,and at the time specified it will pop up a notification in the same way as it does for calendar events and after that it will show the mail in red in the index until it's marked "completed".

He also notes that Reply-By stems from X.400 via RFC 2156 and has indeed been standardised by RFC 4021.

I shall investigate this further when I have time.

NP: Foo Fighters: Echos, Silence, Patience & Grace