Since SSO with Salesforce is case sensitive you need to get the information directory form the Domain Controller

Logon to Domain Controller

Import-Module activedirectory

Get-ADUser -Filter {EmailAddress -like “*lastname*domain.com”} -Properties EmailAddress | Select Name, EmailAddress

If you need assistance setting up SSO – https://developer.salesforce.com/page/Single_Sign-On_with_Force.com_and_Microsoft_Active_Directory_Federation_Services