26: It Can, But Doesn’t

Still hammering on Run Your Own Mail Server.

If you’ve worked with signing protocols like OpenPGP, you’re familiar with digital signatures. You take a chunk of data and sign it. Any alteration to the file invalidates the signature. You might be expecting DKIM to work the same way. It can, but doesn’t.

Traditional mail software has been free to rearrange messages if the programmer thought it necessary or correct. This might include adding or rearranging headers, substituting one kind of whitespac...