Processing the check is IRS's responsibility. If they accepted your check, but do not process it, it is their fault. Once they accept your check, your end of the deal has ended. A while back, I got a notice that I did not pay my state tax.
1 The xiphoid process (Latin: processes xiphoideus) is a small triangular cartilaginous extension of the breastbone.
Other names for the xiphoid process are processus xiphoideus, ensiform or xiphoid appendix. It rests at the 10th thoracic vertebra. It is the tiniest and lowest part of the sternum. Unlike the other two parts of the sternum namely manubrium and body, there are costal cartilages and ribs that are attached to the xiphoid process. 1  Attached to the anterior surface of the xiphoid process are the anterior costoxiphoid ligament and a section of the rectus abdominis muscle.