Mailed postcards on our last trip to Puerto Vallarta back to the US. Unlike the previous year, the local post office had postage and so did the hotel. Closest postage to the actual rate the hotel had were two $7MXN stamps. Note that these were very large for the postcards. Ideally they would have been placed first, then the addresses written.
Took three weeks from the hotel to the cancellation stamp in Puerto Vallarta, and then another two months to delivery in the U.S. But they finally made it!^