An envelope is not simply a small sheet of paper. Its seams, flap and thickness change how it should pass through a printer. The correct direction depends on both the envelope design and the printer's documented path.

Read the diagram for the actual model

Check that the envelope size and construction are supported. Do not assume that a tray accepting the width also accepts the material. HP's guide for the E731 and E786 families, for example, restricts envelopes to Tray 1 and gives different orientations for some pocket and wallet styles. That example should not be copied onto another printer.

In the application, select the actual envelope size and inspect the address layout. Then select the appropriate size, Envelope media type and supported source in the print driver. Keep return and destination addresses within the documented printable area.

If the guide instructs you to send the job before loading a manual feed, follow that sequence. Avoid filling several trays with envelopes in the hope that the printer will choose the right one.

Validate one before the mailing run

First check the layout on a plain-paper proof where practical. Compare the printed address position with the envelope dimensions. Then use one supported envelope to verify the physical feed and final placement.

Inspect the front and back for creasing, smearing, an upside-down address or unwanted printing over a seam. A successful plain-paper proof cannot prove that an envelope will feed correctly, so both checks serve a purpose.

Stop if envelopes catch, wrinkle or show adhesive problems. Consult the media instructions instead of forcing them through or repeatedly increasing thickness settings. Once the result is acceptable, keep a loading note that names the tray, envelope product and flap orientation. Recheck when any of those changes, and keep the remainder of the batch in good condition until needed.

Sources: HP envelope loading example.