This is a Box of 500 Vintage DRG Defiance DL Pocket Envelopes 0 2231 4
They are DL Size, 220 x 110mm.
They say seal-easi but I very much doubt that will still work ! You will probably have to put a bit of tape on !
They will have some discolouration due to age.
I think they are from the 80's.