code:

---

$ObjUser=GetObject("LDAP://"+$Server+"/CN="+$User+",CN=Recipients,OU="+$Site+",o="+$Org)
$oMailbox=$ObjUser.GetEx("otherMailbox")

"mailbox before change:"
for each $value in $oMailbox
 ? $value
next
 $oMailbox[UBound($oMailbox)]="smtp$$xx@@test.dk"
? ? "and after:"
for each $value in $oMailbox
 ? $value
next
 

---

not sure but think it comes to com-object arrays...
try it out but might be you need to find another way to do this