HP Officejet 300 HP OfficeJet Model 330 and Model 350 - (English) User Guide - Page 162

Printing Envelopes With Windows Applications When using the HP OfficeJet to print envelopes from a Windows application, be sure to choose envelopes as the media size (in the Printer Options dialog box). The HP OfficeJet automatically selects the correct Orientation when you choose an envelope media size. The Orientation controls in the HP OfficeJet Printer Setup dialog box are grayed out when you choose an envelope size. You may, however, need to select printing orientation in your software program. Some programs use a print setup dialog provided by Windows to select common printer settings. This dialog does not automatically default to the correct orientation for envelopes. If the Orientation settings are not disabled (grayed out) when you select envelopes, you must select the correct orientation in the software program print setup dialog box. Select Landscape orientation for the HP OfficeJet printer.