Reb Folle Kahn ע"ה relates:
One of the famous Chassidim of the Rebbe Rashab, Reb Shmuel Michel Treinin, lived in Petersburg. Once, one of his grandchildren fell ill, and Reb Shmuel Michel wrote a pan to the Rebbe Rashab and sent it by mail to Lubavitch. He then received a telegram from the Rebbe Rashab summoning him to Lubavitch immediately for a particular reason, so he travelled. When he arrived and came before the Rebbe Rashab, he told tell him about the illness of his grandchild, saying that he had sent a pan to the Rebbe Rashab. He told this because he estimated that the pan had not yet arrived. The Rebbe Rashab said to him, “As soon as a pan is sent, one is already assisted.”
Shemu’os V’Sipurim, Vol. 1, p. 116.
Explanation: Writing a pan is in and of itself a way of a chossid establishing a connection with his Rebbe. Thus, the pan does not need to be seen to arrive for it to be effective. As soon as the chossid writes the pan and sends it, the Rebbe senses it and the chossid is blessed.
Comment: This story is surely very relevant to our time, when we cannot openly see the Rebbe receiving our requests for blessing; although we can bring these requests to the Ohel, one might feel that it does not hold the same sort of as effect and potency as when we were able to receive a response openly. However, this story demonstrates that even without the Rebbe actually receiving the letter, it is fully “registered.” So, too, nowadays—even without receiving an open response, we are confident that the Rebbe has heard our request and is doing his utmost to intercede with Hashem on our behalf.