The post cuff (infraspinatus, teres minor, and posterior capsule) is often the culprit of limited shoulder mobility or shoulder dysfunction. Posterior cuff tightness pushes the head of the humerus anteriorly (forward), which can contribute to myriad shoulder conditions including shoulder impingement, anterior instability, rotator cuff tendinopathy, and general scapular dyskinesis. The best way to tackle post cuff tightness is through the hands (or tools) of a skilled medical professional (i.e. YOUR physical therapist) utilizing soft tissue mobilization techniques. However, if you're looking to work out your post cuff tightness on your own, here's a nice stretch for you.
The sleeper stretch directly targets the post cuff. It's slightly controversial because the glenohumeral position can potentially cause shoulder impingement. SO IF PERFORMING THIS STRETCH HURTS, STOP RIGHT AWAY!!!
Typically the sleeper stretch is performed on your side. This is done to "anchor" the scapula to the table and allow the stretch to actually hit the post cuff INSTEAD OF THE RHOMBOIDS. However, having the shoulder in 90 degrees of horizontal adduction significantly decreases the subacromial space, where you can have shoulder impingement. If that impingement occurs, try the modification shown where I lean slightly away from my shoulder (increasing the subacromial space) while still anchoring my scapula to the table.