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.
When experiencing pain in the lower sternum, where the xiphoid process or lowest point of the sternum is located, you pay be experiencing xiphoid syndrome, according to Wrongdiagnosis.com. Xiphoid syndrome can be associated with gallbladder disease, bone disease and heart disease.