The general rule for email, text, and all other communications I've heard is: "Don't write anything that you wouldn't be comfortable seeing on the front page of the New York times."
Heard that first from a US mil commander who once ran for a minor political office like state rep.
I’ve also been told to preface all of my written communications with “dear lawyers and the FDA” at a job. Not that we did anything illegal, but sometimes you catch yourself writing statements that would be really easy to misconstrue.