Hi all,
I too had a toe out problem. I agree with Heather it has to do with tight hips and ankles. They are tight because the tendons and ligaments are tight. Warm up without stirrups helps to lengthen the ligaments. Then do some quadradept stretches. Bring your heel to your bum, leaving your seatbones on the saddle. Then push your pelvis forward to feel the stretch in your quad. Also lift both knees up as high as you can. No cheating by resting your feet on the side of the saddle.

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And last but not least and the most important exercise...this is the one that truely turned my toes in...
The scissor exercise...it was suggested that I do 200 of these on every horse I rode. I was ridding 5 a day at that time.
Keeping your seatbones in the saddle with even weight on both, hold the pommel and kick back with one leg and forward with the other. Kick back from the hip joint not the knee. This does cause a cramp or two in the beginning. Imagine that you are trying to push the bone in your leg to the back of your thigh. Think toes in while doing this exercise. I got up to 60 per horse. I couldn't go 200...partly because my attention span isn't that long. But my toes now point forward. It is hard work...and I quit this exercise and then start again because it is an ongoing problem. Our outside thigh muscles are weak. The inside thigh muscle is strong, that is what turns the toes out. When you strengthen the outside muscle your whole hip turns in - not just your toes. This is a difficult exercise but it really does work. Good Luck.
Colleen