Vertical Stripe Only On Envelopes

[Gab]

try some rint with ebvelops and stop printing during printing while the encelope is at different points. So you can locate rhwe part that causes the problem (drum, Fusing etc) .
\I bet that hot roller is worn at this place nd doe to pressure line doesn't appear on siple paper. If with the tips of your finger you can sense the line (like it is sculptured|) it is hott roller.

[mikadonovan]

I have Windows 7 Pro x64.

FYI, ALL support (including security updates) for win 7 ended completely last month. Microsoft still offers a free upgrade to windows 10, you might want to use it. It very well may take care of your "lines only on envelopes" issue. There is NO WAY I would run an internet connected machine without updates in this day and age of information theft.