The thickness of envelopes and their ability to fold vary widely. If the total thickness of the stack of envelopes exceeds 12 mm, press down on the envelopes to flatten them before loading. If print quality declines when a stack of envelopes is loaded, load one envelope at a time.
Do not use envelopes that are curled or folded.
Flatten the envelope flaps before loading.
Flatten the leading edge of the envelope before loading.
Avoid using envelopes that are too thin, as they may curl during printing.