The most striking thing to me about IBM memos from this era is just how literate executives were. These days most VPs struggle to write a single sentence worth reading.
If you want to improve your communications - when you finish writing your email, leave it as a draft for 30-40 minutes. Then go back an re-read it with a fresh viewpoint.
If I can suggest - the USAF has a manual for this, which guides you in being clear, concise, and specific:
https://static.e-publishing.af.mil/production/1/saf_aa/publi...