While using Activedirectory as User directory you can configure/map the user-name-attribute with the equivalent Active directory attribute for e.g. email address parameter which by default is set to the UserPrincipalname
Below is the screenshot of the LDAP attributes using the LDAP Browser
Below is the screenshot of the Spotfire Configuration tool, mapping the userprincipal name
If the full email address is required for authentication, disable the option to "Parse User and Domain name" as in the image below