A:Answer As Jimbob says: Sounds like you need to make sure you remove the 8.5 x 11 paper and after inserting the #10 pull the plastic guides in from the side. It should then match the selected paper size. That is if you have changed from A-4 or 8.5 x 11 paper to #10 envelope, with the Print commands. (probably need to change back when done, also?) Default is A-4 paper size.
If the envelopes are set up correctly in the "Main Paper Tray" maybe set up the Paper Size in the print popup dialog. This can be found in either the Printer Assistant or from the dialog box that is found in the Print command of the document (in this case addresses?). Using "Word" to access that, in upper left is "File." Left click that and then left click "Print." Then, in the upper right of the new dialog box, click on "Properties" and in the popup click on "Paper/Quality." In the new popup, click on "advanced" in lower right, which is the dialog to select the #10 envelope. Click OK, OK, etc. (about 2 times) until you back out to the Print dialog box again. At the bottom click print and it should work. Experiment with plain paper cut to the size of the #10 envelopes until you figure it out. The "Printer Assistant" feature for the Envy has similar commands. I don't know if you have to set the paper size back to letter size?
Otherwise contact HP support.