We've got a Phaser 6280 that wrinkles envelopes pretty badly. We've tried various sizes of envelopes, mostly #10.
From searching these forums and doing a bit of Googling it seems that this issue happens often enough on many different printers, but the solution I always read is to lay down the flap in the back of the printer so that the envelope exits the printer in the back and skips the parts of the printer that cause the wrinkles. From what I can tell while examing our 6280, it does not have an option like this.
Any other ideas? For what it's worth, we're using the Xerox Global Print Driver. I've tried configuring both the driver and printer for Envelopes and Thick Card Stock. Wrinkles persist.
Try taking a pen or a pencil and press down firmly and run along the envelope. The goal being to push out all the air and flatten out the envelope as much as possible. You may get a few wrinkles at the end of the enveolope by doing this, but it's probably more acceptable than what you get after printing. As you stated, wrinkles on envelopes is a very common thing.