Set "From" based on "To" when replying

[Simon Campese]

Dear Community,

I've got my own domain and when registering or shopping at some website,
I always use email addresses of the form "websitename at mydomain.org", so
for example I use "amazon at mydomain.org" when shopping at amazon. The
reason for this is categorizing incoming mail on the one hand, and
immediately being able to spot the source of spam on the other hand. 

I would like to implement the following behaviour: When replying to a
mail that has "something at mydomain.org" in the "To"-header, I would like
to have the "From"-header of the reply to be automatically set to this
address. 

Is there some kind of reply-hook in notmuch where one could put an
appropriate function? 


Thank you very much for your help,

Simon