Ink is smudged on envelope. How do I stop that from happening?

I bet you're printing in Black,
what happens is when black is selected, the 3 colored drums lift up 2 mm annd only the K drum is engaged, amd there is no static in the transfer belt under the CMY drums.
envelopes have air in them and can bounce along the bely after the black has printed, and seeing the toner is powder and not yet fused on, the toner touches the cyan drum as the envelope hits the fuser entry point as well as dragging on the Left transfer belt Blue lift handle(take out the belt and spring the handle off).
If you open the lid in this print mode, and lift out the cyan drum, turn it over and pull back the cover for the OPC drum, you will see the black toner on the green drum.
FIX 1. In the art work place a tiny dot of yellow. this will run the print mode in color and enagage all the drums. gaurantee your print will be fine, and know one ever sees that yellow dot.Problem is, this then runs down your CMY drums for black only printing.

FIX2.
If you have a later machine, downlaod iQueue from Xante.com (free) fantastic software. and get the machine updated with the latest X1.11 firmware from your dealer.
This allows with iQueue, to set the machine to print Black only, and you run the machine without the CMY drums installed....it works, it's great...

Im having the same issue but with 4 color printing on my envelopes

Our solution was to print a black color envelope with simple logo and text as rich black and open the envelope flap.It seemed that the toner smudge was due to to much air in the flap.Doing this allowed for the envelope to be printed flat.Were still not sure how to remove the extra air so we can print flap folded. Any ideas?