Brother MFC640CW Service Manual page 26

Do not use paper or envelopes:
that are damaged, curled, wrinkled, or irregularly shaped
0.08 in.
(2 mm)
or longer
that are extremely shiny or highly textured
that were previously printed by a printer
that cannot be arranged uniformly when stacked
that are made with a short grain
Do not use envelopes:
that are of a baggy construction
that are embossed (have raised writing on them)
that have clasps on them
that are not sharply creased
that are preprinted on the inside
0.08 in.
(2 mm)
or longer
2- 5
Confidential