Every letter that is sent to someone, whether by email or by surface mail, is also an exchange of forces on the inner planes, which can be detected by someone who has become conscious of his inner being (i.e. astral body).
In this passage, Sri Aurobindo explains the phenomenon to a disciple whose consciousness had developed to sense this possibility.
As for not having it always, it is because there are parts of the being that are still unconscious or perhaps states of unconsciousness come. For instance, people write letters to each other, but they are quite unconscious that they are exchanging forces in doing so. You have become conscious of it, because of the development of your inner consciousness by yoga – and yet there are likely to be times when you still write from the external awareness only, and then you will see the words only without being aware of what is behind. So, owing to the development of the inner consciousness, you are able to understand what contacts are and get the true contact, but at times the external consciousness may be stronger than the inner one, then you are no longer (for the time being) able to get the contact.
This is an example from the life of Mother Mirra Alfassa. She sensed that a letter from Indira Gandhi (India’s third Prime Minister) was coming before she received it.
And all night long (or a good part of it in any case), Indira Gandhi’s thought was here, clinging to me (Indira Gandhi is Nehru’s daughter), and the jewelry was sent to her.[[Mother sent a special messenger to Delhi with a symbolic gift of 925 grams of gold (some from her own jewelry), as a contribution to national defense. ]] It was handed over to Nehru, who passed it on to Indira.[[ Indira Gandhi will come to power four years later, in January 1966. ]] And she wrote me a letter I received yesterday – a very (Mother searches for the proper word) … a very amicable letter; a letter from someone who has understood that this gift was an important element – not on a worldwide level (!), but because it was important that people know I have made a gesture of collaboration. But it didn’t end there. The letter came yesterday; generally, of course, when I see a letter coming, I see it BEFORE receiving it; but here it was SHE, she herself, thinking [of Mother], thinking, thinking, thinking over and over again. (With Nehru, it’s always very blurred: he doesn’t have sufficient mental power for his position, he lacks the required strength of mind, so it’s always hazy; when you tune in to him, that’s the impression you get – blurred gesture – not solid.) But with her, it kept coming and coming and coming. They must be feeling … or beginning to feel that something other than what they have is required.
The Mother, Mother’s Agenda: November 20, 1962