$EASMailboxes = Get-CASMailbox -Filter {HasActiveSyncDevicePartnership -eq $True -and DisplayName -notlike "CAS_{*"} | Get-Mailbox

$EASMailboxes | Select-Object SamAccountName, DisplayName, PrimarySMTPAddress, @{Name="EASDeviceCount";Expression={(Get-ActiveSyncDevice -Mailbox $_.Identity).Count}} | 
Export-CSV c:\scripts\output\EASMailboxes.csv -NoTypeInformation