I received a bill-pay check from my sister and it came in a very non-descript envelope - posted with 'pre-sort' postage.

I often throw away such envelopes as junk mail, so I can see some landlords perhaps doing the same.

Best to either let the recipient know its coming (as she did) and to be on the lookout for a non-descript envelope with payment, send a bluebird check in your own hand-addressed envelope with a stamp, or as suggested above, withdraw to your own account and send your own check from your own account.