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.
Generally, xiphoid pain is triggered by harmless activities such as lifting heavy objects or bending and even large meals can start pain attack or xiphoid process. Diseases, medical conditions, medication to certain drugs, and toxins are also among the common causes of pain in xiphoid process.