We are making a move from Reddfish Listserver (horrible - don't even Google it) to Mailman. Reddfish "integrated" with Exchange by working with AD groups and contact types. During this migration, I have to get the current lists into mailman which means I have to get a nice clean list of line seperated email addresses to feed into Mailman. Here is the code I use to get this to work. Very simple, but I hope it still proves useful.

add-pssnapin -erroraction silentlycontinue Microsoft.Exchange.Management.Powershell.Admin 
 
$listname = 'You List Name Here'
$filename = "c:\\$listname.txt"
 
$listmembers = get-distributiongroupmember $listname
 
foreach ($member in $listmembers) {
  write-output $member.primarysmtpaddress.toString() >> "$filename"
}