best solution TNX to Drew Chapin and all of you too:
I just want to add that if you don't inheritently know the name of a domain controller, you can get the closest one, pass it's hostname to the -Server argument.
$dc = Get-ADDomainController -DomainName example.com -Discover -NextClosestSite
Get-ADUser -Server $dc.HostName[0] `
-Filter { EmailAddress -Like "*Smith_Karla*" } `
-Properties EmailAddress
my script:
$dc = Get-ADDomainController -DomainName example.com -Discover -NextClosestSite
Get-ADUser -Server $dc.HostName[0] ` -Filter { EmailAddress -Like "*Smith_Karla*" } ` -Properties EmailAddress | Export-CSV "C:\Scripts\Email.csv