Secret correspondence was divided into several series. Particularly important - a series of "K" consisted of orders, correspondence and reports of a top secret character. This applies primarily to the Politburo of the materials, and the Organising Bureau of the Central Committee Secretariat. Correspondence "K" series should only pass into the hands of the recipient, which in this case was required to leave the shell on receipt of the package. In the absence of the addressee, they returned back to the machine to send them feldsvyazi. Exceptions are allowed only in relation to substituents of these individuals, their personal secretaries or other persons, if they had written authorization directly from the recipient. Addressing the establishment of the correspondence series "K", without specifying the destination names were forbidden. The envelopes with receipts after delivery to the addressee to return transferred messenger feldsvyazi OGPU. In no case shall delay the addressee envelopes a day, not to mention the non-return of those  92. And, the cipher telegrams from Stalin June 21, 1922 were instructed to return them necessarily stitched for wax seals and transmit directly to the head of the Bureau of the Central Committee Secretariat, under the personal signature  93.