[ This article is posted at ElMajdal.Net website : http://elmajdal.net/ExchangeServer/How_to_Change_OWA_Forms-Based_Logon_Option_in_Exchange_Server_2010.aspx ]
The three options for the default sign-in format are :
FullDomain : This is the domain and user name of the user in the format domain\user name. For example, for a user named Tarek.Majdalani in the domain elmajdal, the sign-in would be elmajdal\tarek.majdalani PrincipalName : If user principal name (UPN) sign-in format is specified, the User Name field on the Outlook Web App sign-in page guides the user to enter their e-mail address. For example, tarek.majdalani@elmajdal.com. UserName : This is the user name only and doesn't include the domain name. For example, tarek.majdalani
These options change only the text on the Outlook Web App sign-in page. They don't cause a particular format to be required. The user can use any of the standard sign-in formats regardless of the text on the page.
To change OWA forms-based logon option, follow the below steps :
Open Exchange Management Console, and then from the left side pane, expand Server Configuration and click on Client Access
From the middle pane, and under the Outlook Web App tab, right click on owa (Default Web Site) and click Properties
The owa properties will open, click on the Authentication tab As you can see, under the forms-based authentication section, three authentication options available:
Domain\user name
User principal name (UPN)
User name only
The default logon option is by typing DomainName\UserName and this is how it looks like on OWA It prompts the user to enter : elmajdal\tarek.majdalani for example.
Summary
Forms-based authentication gives you three options for the default sign-in format. These options change only the text on the Outlook Web App sign-in page. They don't cause a particular format to be required. The user can use any of the standard sign-in formats regardless of the text on the page.