"The most heated bit of letter-writing can be a wonderful safety valve – providing the wastebasket is somewhere nearby." Bill Wilson
It's good to get anger out in a healthy harmless way. Journaling is one such way to vent. Anger let out against people causes retaliation. Retaliation causes you to increase your anger when your goal in sobriety is to decrease it. Dealing with retaliation complicates our lives when our goal in sobriety is to simplify our lives. Foisting anger on others creates a bad spiritual balance (karma). Bad spiritual balance is also bad for our sobriety. Remember today that it is your goal to do what's good for sobriety, not what is necessarily good for our ambitions, ego defenses or selfishness.
Get the anger out by journaling. But don't let the anger interfere with your life by sending that journal to the subject of your anger. Wait until anger passes to communicate with others.