HP LaserJet 5100 Printer series - Manual (Page 128)

A-12 Specifications
ENWW
Envelopes with Double-Side-Seams
Double-side-seam construction has vertical seams at both ends of
the envelope rather than diagonal seams. This style may be more
likely to wrinkle. Be sure the seam extends all the way to the corner
of the envelope as illustrated below.
Figure A-1 Envelopes with Double-Side-Seams
Envelopes with Adhesive Strips or Flaps
Envelopes with a peel-off adhesive strip or with more than one flap
that folds over to seal must use adhesives compatible with the heat
and pressure in the printer. The extra flaps and strips might cause
wrinkling, creasing, or jams.
Acceptable
Unacceptable