Write the angry text. Then wait an hour before you send it. You’ll edit most of it out.

Writing it and sending it are two different needs, and only one of them is urgent. The writing discharges the feeling, which is why it helps immediately; the sending is the part you cannot take back. An hour later the true part is still true and the rest has stopped seeming necessary, which tells you what the message should have been.

Store it somewhere it cannot be sent by accident, in notes rather than in the message box. Set an alarm for an hour and go and do something else entirely. Then read it back and keep only the sentences you would say to their face.