Maybe I am missing something, but since this PS1 script must be run in the source domain, how is it any different from the following VBScript (barring the piping of a user list)
DIM strUserDN '*** This is the distinguished name of the user (string)
DIM objUser '*** Object variable for containing the user
DIM strEmailAddr '*** Populate with the external email address of the mail-enabled user
'*** Set variables
strUserDN = "[Distinguished Name of Account]"
strEmailAddr = "[email address]"
'*** Get user object
wscript.echo "Connecting to user " & strUserDN
Set objUser = GetObject("LDAP://" & strUserDN)
'*** Wipe out the existing Mailbox
wscript.echo "Removing mailbox"
objUser.DeleteMailBox
objUser.SetInfo()
'*** Okay, now let's mail-enable it
wscript.echo "mail-enabling the user with address: " & strEmailAddr
objUser.MailEnable strEmailAddr
objUser.Put "internetEncoding",1310720
objUser.SetInfo()