[exim] Smarthost with smtp-auth

My wonderful ISP has suddenly (like today I think) decided that I can no
longer send any mail anywhere on port 25, including there own mail servers.
They do however allow it through port 587, with smtp-auth. This breaks my
smart host and I cannot find how to setup the smart host to send smtp-auth.
I know I'm probably just missing this somewhere, can someone point me in the
right direction please?

Thanks,

Andrew