[Evolution] Filters for Outgoing mail

[Richard A Downing FBCS <geek109 hotmail com>]

I want to try adding a hashcash (www.hashcash.org) header to mail that I
send from evolution-1.4.  I note that there is an outgoing filter 'pipe
message to shell command', but can find no specification for this
anywhere (it's certainly Not a FAQ!).
Tests reveal that the shell command gets the message as a $1, which will
let me run hashcash OK, but how do I get the message, with an added
header, back into evolution for transmission?
I guess I'm also asking 'is there a technical specification for filters
on evolution?', as well as this specific question.

Regards,
Richard.
-- 
Richard A Downing FBCS  http://www.109bean.org.uk
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