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.
The styloid process is a slender pointed piece of bone just below the ear. It projects down and forward from the inferior surface of the temporal bone, and serves as an anchor point for several muscles associated with the tongue and larynx. 1  Its proximal part (tympanohyal) is ensheathed by the vaginal process of the tympanic portion.