[Enigmail] Expect signature header proposal

[Eitan Adler]

John W. Moore III wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA512
> 
> Robert J. Hansen wrote:
> 
[snip]
> Given the extremely small percentage of _all_ Email that is
> cryptographically Signed the appearance of this 'Warning' on 99% of
> received Email would quickly become extremely annoying.  

This message would only appear for recipients that you specifically 
enable it for (I dropped the header idea a few emails ago).
Alice sends (unautomated) signed message to Bob "I always sign my 
messages - just letting you know".  Bob who gets many messages from many 
people each day goes to his address book and clicks the "this sender 
always uses a key" for Alice.  Claire sends an unsigned message 
pretending to be from Alice an Bob gets a message that the message is 
missing a key.

Tradeoffs: Extra UI space, one more paragraph in the documentation, more 
complex code to maintain (possibly the worst of the three).