Routing all email to a given domain through a relay

[sjau]

Hi there

Currently I have problems with Yahoo as it defers all email. This goes back more than a week ago when one of the accounts got abused for spaming. Ever since, Yahoo has blacklisted my IP and all email sent to yahoo is being deferred.

So I though I could setup a email routing that all email to Yahoo goes through another server. It seems ISPC does have email transport available but I don't quite understand it.

Traditionally I'd make an entry in the postfix main.cf to use a transport map.
In the transport map I'd enter something like: yahoo.com :[myother.server.com]
And finally I'd use smtp_sasl_password_maps to create an entry for myother.server.com with username and password.

However in the ISPC I don't see any kind of username password entry.