Outllook 2013 and multiple accounts

Hi!

We have Exchange 2003 in our domain but MS Office 2013. We know outlook 2013 cannot work with Exchange 2003 but one of our domain users needs to connect to Exchange 2013 and 2010 outside of the company network. When we open outlook 2013 on his pc it tries to connect to exchange 2003 automatically. If we select manual configuration and enter the credentials for Exchange 2010 and 2013 accounts it does not connect and keep asking for username and password.

If we use a local user instead of a domain user account in this pc then he is able to connect.

Any Suggestions?

Thanks.