I have had the issue I have 3 PO in a 5 min radius so one of the post offices said the best way to send them is use greeting card envelopes because you don't need to fold them as small so they slide thru the slot and the thickness makes the difference. If there are lots of seams or I do embroidery that also makes them thicker or if you don't cut the ziplock part off the Baggie hope that helps. And it was 20 cents extra for hand canceling them which I always do.