E-Mail Router: Accessing Exchange via https intern / extern

Hello there

I am configuring an E-Mail Router for a Customer. The problem is, he has a SSL Certificate for *.customer.ch on the Exchange Server, https://owa.customer.ch has its target on a TMG with web based authentication. The E-Mail Router is not able to pass authentication, Error 405 - Method Not Allowed. From internal, the link to the Exchange Server is exchange.customer.local and not .ch.

The E-Mail Router wants to have also a https://-connection, but I cannot make a second SSL Certificate on the Exchange Server.

How can I achieve a solution here?

thanks

Raffi