routing according to sender domain, not recipient domain

[Patrick Chemla]

Hi,

I would like to relay messages to specific MX servers according to 
sender domain, not recipient domain.

I saw the primitive sender_dependent_relayhost_maps but I don't know how 
to use it.

Should I create a list and postmap it and set a line in my main.cf like :

sender_dependent_relayhost_maps = hash:/etc/postfix/senderdomainroutes  ?

Thanks for help

Patrick
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