What happens if I dont mail in my tax form

If you owe tax, there are penalties up to 25% of the tax due, plus interest from the date due until the date paid.

If you file and don't pay, you avoid the 25% failure to file penalty. You can work out a payment agreement with the IRS.

If the IRS thinks you might owe money, they will contact you and request a return.  If you don't comply, they can assess and collect whatever tax they think you owe.

You do have appeal rights, but you are far better off filing a return.

To file a tax return, you must either efile it or print and mail it yourself.  If you meet the requirements to file a tax return, you are required by law to file it.