E-mail is not private.
Once the Send button is hit it is virtually uncontrollable.
It is discoverable.
It is evidence.
Treat it as a business record.
“Grind your axes” elsewhere.
Don’t speculate about things you do not know.
Don’t be “cute.”
Don’t use shorthand.
Avoid “inflection” through punctuation marks.
Think before you hit the Send or Forward button.
Read it two or three times before you Send it.
Try to envision it in the hands of an enemy.