[bcl]

This would work if you could search all of your tweets. I don't think that is currently possible, is it?

It also assumes that twitter is going to be around when you finally need the timestamped hashes, and that you can prove that twitter (or any other service for that matter) can't have back-dated hashes inserted.

Posting to a usenet group, like alt.test, where independent systems store and timestamp the message would be a better idea.

[mthoms]

Why not just use multiple webmail services?

[pmjordan]

Email timestamps are laughably easy to fake.

[mthoms]

Surely Google et al, record the actual arrival time of the email in the headers do they not?

If not, then I'm sure they do in their logs.

[pmjordan]

What stops you copying in a crafted email via IMAP, though?