Can I verify that I filed a Form 1041 Estate Tax Return last year? I prepared it, and have the K-1 distribution form, but I can't remember if I mailed it to the IRS.

This is a fiscal year 1041, needing to be mailed in by mid-November of 2015. No tax was due for that return itself. I had it completed by mid-March of 2015, but cannot remember if I sent it in then, or simply forgot about it.