"Know that a word suddenly shot from the tongue is like an arrow shot from the bow. Son, that arrow won't turn back on its way; you must damn the torrent at its source." - RumiI see it time and time again in the online world. Discussions getting heated because someone said something that someone else didn't agree with or took the wrong way.
Don't jump to conclusions, just because you've read something that presses your buttons, particularly if you don't know the sender or the personalities involved. Re-read the text but take a different viewpoint. How would you read and interpret this message if it was written by a friend?
Remember that tone, feelings and the more subtle aspects of humour are difficult to convey in the written word. The same sentence read with different intonation and emphasis can be interpreted completely differently.
That said - if you have the habit of putting your foot in it it's worth spending a few minutes to think before you speak. At least take time to read what you've said before you hit send or be prepared to deal with the effect should the arrow find a different 'target' from what was intended.