Envelopes & Labels Options

The Envelope Address style, which is used for the address of an Envelope, contains a Frame.  Modify the width of that Frame in the Modify Style dialog for the Envelope Address style.

 

Easiest way to access that style to modify it is to add an envelope to the document and then with the cursor in the address, press Ctrl+Shift+s to display the Apply Styles dialog in which you should see Envelope Address as the style that is in use.  Then click on the Modify button in that dialog.

Envelopes are formatted using the Envelope Address and Envelope return paragraph styles from the active document which in turn were derived from the template that document was created from. As has already been reported the Envelope Address paragraph style features a frame with fixed dimensions. You can modify that frame size and save the results to your template and that will then be used next time - see http://www.gmayor.com/changing_envelope_layout.htm. If you set the width of the frame to 'Auto' then the lines will never wrap as long as there is space on the envelope for the frame, so it is perhaps better to set its width to a measurement that will allow your longest address lines to fit.

When modifying styles don't forget top check the box 'New Documents based on this Template' or the changes will apply only to the current document (which appears to fit the issue you describe in your latest reply).

Alternatively, you could use a template for your envelopes, formatted as you wish. To facilitate that see http://www.gmayor.com/Envelope_Label_Add_In.htm  which comes complete with a sample envelope that you can modify to your taste.