Problem Printing Envelopes - toner dirt on envelope M426fdw

[s2kohio]

The printer works fine until I need to print an envelope (I use No.10 envelopes).

When I print an envelope, the printer leaves toner dirt  on the envelope to the left of the address to which I am sending the mail. 

No other time is there dirt on any print. Please help me. I just bought this printer in July 2019 and since I got it the envelope printing, which I do once a month, is very unprofessional looking.

if it needs to be fixed how does a tech come to my office to clean it or replace whatever defective part is in the printer?  I think under the first year there is some kind of on-site warranty???? 

Thanks to anyone responding, most appreciated. 

[Apone]

make sure the tray you're printing the envelopes from is set to the correct paper type, that way the fuser will reach the correct temp to bind the toner to the envelope.  if the wrong paper type is selected, the printed text/image can smear or look dirty. 

[s2kohio]

I use the manual envelope feeder. So it isnt a problem with the tray. The printer is set correctly for number 10 envelopes. 

any other thoughts? 

[Repairatrooper]

You have it set for Envelope size, but do you also have the paper type set for envelop? Are these OEM toner or 3rd party? Some brands of envelops have more issues than others.