I've got two Mailboxes from two Exchange Servers. One works but the other won't. I don't know what the problem is, maybe you can help me...

When I add a new 'automatic' Account, it searches the server and I get the message "Authentication failed. Check your account information and try again."

When I set up the server manually, I get the message "Outlook was redirected to ... autodiscover.domain.tld..." what is ok, but the Mail-Account has a yellow light and no folder is visible for this account. 

Yes of course, it's possible that the Exchange-Server makes the problem... but why does it work with my Mail.app??? Does Microsoft support the Mail.app (on my OS 10.8 and iPhone) more than his own product?!?!

I'm pretty nerved and confused. I hope somebody can help me.

Regards