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At or very close to the equinoxes, the sun will rise pretty much due east (within maybe 2 degrees allowing for atmospheric refraction).
No matter where you are in the world, at least from local spring through local autumn between the equinoxes, the sun *will* be able to cast a shadow due east or west. From local autumn through local spring, (for southern latitudes) the sun has to rise between east and south, and sets between west and south, never passing the east-west line so during local winter you can never get a shadow falling true east or west.
It's not as easy to calculate as north-south at local solar noon, as you start getting into fun trigonometry, but any planetarium app for PC or smartphone should allow you to check it out. Look at the alt-az coordinates of the sun, and when the azimuth is at 90 or 270, the shadows will be due west when sun is at azimuth of 90, and due east when the sun is at an azimuth of 270.
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