send-hook pain ....

["Wilkinson, Alex" <alex.wilkinson@xxxxxxxxxxxxxxxxxxx>]

Hi all, 

I'm wanting to set up a simple send-hook that has the behaviour of doing
various things upon replying ('r') to a messge with a particular 'Subject' 
string.

e.g

send-hook '~s ^Critical\ Backup\ Errors$' 'my_hdr To: user@xxxxxxxxxxxxxx'

This simple send-hook does not work. I have checked the syntax a million times
and it seems to be correct. The behaviour that I see when I hit the reply key is
that the reply message 'To:' header is still replying to the original sender.

Am I missing something obvious ?

Thanks
 
 - aW