Hello and thank you for help.
I started an exchange migration, right now both server are up and running. Owa is working fine, ECP is working fine, I can connect to outlook via phone and send emails.
I also created a signed certificate, which is working.
Now my problem.
Exchange 2013 had different host names for internal and external.
Internal mail.contoso.local
External exchange.contoso.eu
Using IIS I created a signed certificate over a CA server for mail.contoso.local. Both at the same time, not working.
So I made a split DNS entry for exchange.contoso.local and added the internal Ip of Ex 2013, alongside autodiscover. I also changed autodiscover _tcp entry in the old DNS forest, the standard one.
Changed all internal virtual folders to match the external one, also for outlook anywhere and for autodiscover.
If I try to add a mailbox to outlook I receive a certificate error which shows the old address, mail.contoso.local...why??
Also, much weirder, I also get a certificate error for autodiscover.contoso.eu, so not exchange.autodiscover.contoso.eu, from an unknown wildcard certificate...where does THAT come from?
Right now I am a bit scared in moving all mailboxes and uninstalling the old exchange. Sorry for the long post, I had many issues with this (as it is my first time doing a migration..or exchange in general) in the last couple of nights. Who needs sleep?