Totally Cut Off from the Rest of the World
Once you step aboard a submarine, you should get used to the idea that communicating with your loved ones will be conducted in a somewhat different manner. No mail carrier is going to go to extraordinary measures to travel across the ocean just to deliver your mail to your loved ones, and the same is true in reverse (obviously). The only time you will be able to send or receive mail is when the submarine emerges from the depths and returns to the surface.
The crew of the submarine is continuing their efforts to prevent themselves from receiving a signal that is being relayed by the other craft. Because of this, it is essential to be aware that keeping a connection with the outside world while confined within a submarine may at times be difficult. This is something that should be kept in mind at all times.