Im trying to set the relayhost of a postfix server based on the user sending an email.

I think that you can set witch smtp server to relay a message based on a destination using the transport_maps option (where destination domain is example.com message will be sent through smtp.example.com) but i want to be able to select the relayhost based on the sender.

For example: user(at)random.com sends message to user(at)example.com
because the sender's domain is random.com use smtp.random.com)

Is what im trying to do possible?
Is there something similar to what im trying to do?