Doctor Who Weekly Issue 1 (in-universe)

The Fourth Doctor once wrote a letter on 42 Paztenmber (relative to 1845 "Earth-time"), and delivered it to a post office on Ganymede, to ensure that his letter would reach Doctor Who Weekly in time to be printed in the 1st issue. The Doctor asked his readers if they enjoyed the first issue, and if so, to send in letters of their own to his "Terra-bound collegues".

In a second letter, the Doctor gave instructions on how to use the rub-down action transfers included in the 1st, 2nd, 3rd and 4th issues of the magazine. (PROSE: A Letter from the Doctor)