This PowerShell code write all users from a specific SharePoint Group to a CSV-File.
Get-SPSite http://urlofsitecollection |
Select -ExpandProperty RootWeb |
Select -ExpandProperty Groups |
Where {$_.Name -EQ “Specific Name of the Group“} |
Select -ExpandProperty Users |
Select Name, Email | Export-csv -path D:\myPath\Groupmembers.csv