dim address_on as string 'current address
dim names as string 'concatenate list of names
dim in_list_already as boolean

    For address_row = 1 to range().end(xldown).row
    'loop through addresses
        address_on = Range("Column" & address_row).value
        names = ""

        'First check if address_on is already in destination list?
        in_list_already = false
        for check_row = 1 to range("Destination").end(xldown).row
            If range("Destination Col" & check_row).value = address_on then
                in_list_already = true
                Exit for
            End if
        next

        if in_list_already = false then
            'Find all names that have this address
            for name_row = 1 to range().end(xldown).row
                If range("Address Column" & name_row).value = address_on then
                    names = names  & Range("Name Column" & name_row).value & ","
                End if
            next

            'remove last comma
            names = names.remove(Len(names)-1,1)

            'add to list
            Range("Column to insert to 1" & next_slot).value = names
            Range("Column to insert to 2" & next_slot).value = address_on

        End if

next