This seems to be a command and thus the imperative. I thought the imperative formal was No escriba.. and the informal was No escribe.... This does not seem to be subjunctive or there would have been a question mark at the end..as in but not a direct translation...you're not writing that letter! with the feeling of irritation etc. Any Spanish natives who can clarify? Thanks
That's right tessbee. When in doubt, check the conjugator.
(The affirmative and negative Imperative is at the bottom of the list. )