Which version of Kerberos do I use?

Hi,

We are using a single-sign on software from Evidian.
We've noticed that on our Windows 7 x86 machines, the user is not automatically identified by Evidian when logging in with firstname.lastname@domain.com". The user then have to retype his password in the Evidian window.

On ther other hand, when logging in with the short username, the Evidian engine recognises the account and automatically identifies the user.

I believe this is due to the way Kerberos is used.

I've read years ago the differences between logging in with  "firstname.lastname@domain.com" or the short username, but I do not find the information back on the Net.

Could someone refresh my memory and let me know what are the difference for Kerberos between the long and short username?

I've already found this (http://technet.microsoft.com/en-us/library/cc772815%28WS.10%29.aspx) but it doesn't say whether using the short or long username make a difference or not

Thanks