powershell populate a validate set from script

I waht to streamline a bit of a function with a validate set. Using GShell I can get each of the groups email addresses from the Google email domain as follows

(Get-GAGroup-all).email

What I would like to do is have this code populate a validate set on the custom function below (what I have is wrong I know) so I don't have to look at my admin console to see what the group names are

functionGet-GoogleGroupMembers{[CmdletBinding()]Param(# Param1 help description[Parameter(Mandatory=$true,ValueFromPipelineByPropertyName=$true,Position=0)][ValidateScript({(Get-GAGroup-All).email})][string]$Group="")(Get-GAGroupMember-GroupName$group).email}