Ink flakes off envelopes. No problems with sheets of laser paper.

I agree with Brian Lee on his first point. When the envelope bends slightly as it goes through the rollers, it deforms and a part will be raised higher than normal. That part will brush the underside of the print heads and give you the black smudge. You will probably hear a slight swishing noise as the envelope prints. That is the sound of the heads brushing the paper.

The best solution for this is to print labels and stick them on, or to use windowed envelopes and print the information on the letter or form so that it shows through the window. Hope this helps.

You need to make sure the paper size and that of the printer matches in the dialogue box.
i.e assuming you a printing an envelop DL size, make sure your envelop is the exact size you choose in your page layout.
secondly, open the properties in the printer dialogue box, where you have letter, change the default "letter" paper to you envelop size.
Note: if your envelop size is not accurate and the actually printed, you will still receive "incorrect paper size" error. At this point I turn of mine and turn on again.

BYPASS TRAY is sed when printing onto paper with a size not loaded into a paper tray or onto thick paper, overhead projector transparencies, postcards, envelopes or label sheets Can be loaded with up to 150 sheets of plain paper, 50 overhead projector transparencies, postcards, label sheets or sheets of thick paper, or 10 envelopes referred to as the "bypass tray" throughout the manual. (See page 2-60....ATTACHED )
ftp://207.18.56.26/software/BPG/Userbizhub200250350CopyOperPh2_5.pdf

Here are "little" specification:

Body installation method desktop page printer
Photosensitive medium OPC drum
Exposure method semiconductor laser
Development method Toner projection development
Transfer method by roller
Separation method by curvature
Cassette pickup method by pad
Multifeeder pickup method by pad
Drum cleaning method by blade
Fixing method on-demand
Delivery method face-down/face-up
Toner supply type by toner cartridge
about 6000 prints (A4, single-sided; at 5% image ratio)
Warm-up time in standby: 0 sec (at power-on: 10 sec or less)
Print area top: 5 mm; bottom: 5 mm; left/right: 5 mm (if envelope, top, bottom, left,
right: 10 mm)
Printing resolution 600dpi
First print time 9 sec or less (approx.; A4)
Print speed (A4) 21 pages/min (approx.)
Cassette paper size A4, B5, A5, Legal, Letter, Executive
Multi-purpose paper size A4, B5, A5, Legal, Letter, Executive, Envelope DL, Envelope COM10,
Envelope C5, Envelope Monarch, Index Card, Custom Paper Size (width
76.2 to 215.9 mm, length 127.0 to 355.6 mm)
Cassette paper type plain paper (64 to 90 g/m2), heavy paper (91 to 120 g/m2), recycled
Multi-purpose paper type plain paper (64 to 90 g/m2), heavy paper (91 to 163 g/m2), recycled
paper, transparency, label paper, envelop (DL, COM10, C5, Monarch,
B5)
Cassette capacity 250 sheets (approx.; plain paper, 64 g/m2)
Multi-purpose capacity 1 sheet
Delivery tray stack 65sheets (Face-down) /1sheet(Face-up Output Slot)
Memory 8 MB (internal; no optional memory available)
Operating environment
(Temperature range) 10 to 32.5 deg C
Operating environment
(Humidity range) 20% to 80% RH
Noise 52.8 dB or less (during printing; based on ISO9296; announced noise
emission)
Power supply rating AC100V±10% (50/60Hz ±2Hz)
Power consumption (Maximum) 790W or less (approx.; 20 deg C; for input of rated power supply;
including peak value lasting 1 sec or more)
Dimensions 370 (W) x 375 (D) x 258 (H)mm
Weight printer: Approx;11kg; toner cartridge: Approx,0.8kg(2.5K)
Option paper feeder

Most laser printers have an "S" paper path. They cannot help bending paper. I would suggest you print lables instead of envelopes if you send several letters. If you only send 1, hand address the envelope. Not elegant ut it works.

Hello there,
If the paper is lodged too far into the printer and can't be removed: Press the power button to turn the printer off. 
Pull firmly on the paper to remove it. If you can't reach the paper because it is too far in, raise the front cover and remove the paper from the front of the printer. 
Close the front cover. 
Press the power button to turn the printer back on. 
Resend your document to print.

Ensure that: 
The paper is a recommended paper for Laser printers. 
You do not force the paper down into the printer when you load it. For example, if you are loading letter or A4 size paper, the top edge of the paper should extend above the top of the sheet feeder. 
The printer is on a flat, level surface. 
The left paper guide is against the side of the paper. 
You do not load too much paper in the sheet feeder. Depending on the thickness of your paper, the sheet feeder can hold up to 100 sheets of paper. 
The left paper guide does not cause the paper to bend in the sheet feeder. 
Your printer feeds regular paper as expected. If regular paper feeds without causing problems, load the envelopes vertically against the right side of the sheet feeder. Make sure the paper guide is against the side of the envelopes. 
Envelopes or the appropriate specialty papers are selected in the printer driver. 
You are using a paper or envelope size supported by your printer.
do not forget to rate this solution....good luck

thanks for using FixYa

 Hello there,If the paper is lodged too far into the printer and can't be removed: Press the power button to turn the printer off. 
Pull firmly on the paper to remove it. If you can't reach the paper because it is too far in, raise the front cover and remove the paper from the front of the printer. 
Close the front cover. 
Press the power button to turn the printer back on. 
Resend your document to print.

Ensure that: 
The paper is a recommended paper for Laser printers. 
You do not force the paper down into the printer when you load it. For example, if you are loading letter or A4 size paper, the top edge of the paper should extend above the top of the sheet feeder. 
The printer is on a flat, level surface. 
The left paper guide is against the side of the paper. 
You do not load too much paper in the sheet feeder. Depending on the thickness of your paper, the sheet feeder can hold up to 100 sheets of paper. 
The left paper guide does not cause the paper to bend in the sheet feeder. 
Your printer feeds regular paper as expected. If regular paper feeds without causing problems, load the envelopes vertically against the right side of the sheet feeder. Make sure the paper guide is against the side of the envelopes. 
Envelopes or the appropriate specialty papers are selected in the printer driver. 
You are using a paper or envelope size supported by your printer.
do not forget to rate this solution....good luck

thanks for using FixYa

If the paper is lodged too far into the printer and can't be removed:
Press the power button to turn the printer off.
Pull firmly on the paper to remove it. If you can't reach the paper because it is too far in, raise the front cover and remove the paper from the front of the printer.
Close the front cover.
Press the power button to turn the printer back on.
Resend your document to print.

Ensure that:
The paper is a recommended paper for inkjet printers.
You do not force the paper down into the printer when you load it. For example, if you are loading letter or A4 size paper, the top edge of the paper should extend above the top of the sheet feeder.
The printer is on a flat, level surface.
The left paper guide is against the side of the paper.
You do not load too much paper in the sheet feeder. Depending on the thickness of your paper, the sheet feeder can hold up to 100 sheets of paper.
The left paper guide does not cause the paper to bend in the sheet feeder.
Your printer feeds regular paper as expected. If regular paper feeds without causing problems, load the envelopes vertically against the right side of the sheet feeder. Make sure the paper guide is against the side of the envelopes.
Envelopes or the appropriate specialty papers are selected in the printer driver.
You are using a paper or envelope size supported by your printer.

Here ya go...

Tray 1: (standard) 16 lb. Bond – 80 lb. Cover (60 – 220 gsm), coated, Phaser High Resolution Photo Paper, labels, envelopes, business cards, Phaser Professional Solid Ink Transparencies, Phaser Weatherproof Paper, Phaser Postcards, Phaser Trifold Brochures. Media sizes: A/Letter, Legal, Executive, Statement, US Folio, A4, A5, A6, B5 JIS, B5 ISO, 3 5 in. Index Cards, custom sizes; Envelopes: #10 Commercial, DL, C5, #5 , #6 , Monarch, Booklet, Lee (A7), Choukei 3 Gou, Choukei 4 Gou, custom.
Tray 2: 525-sheet tray (standard) 16 lb. Bond – 28 lb. Cover (60 –122 gsm), coated, Phaser High Resolution Photo Paper, labels, envelopes, Phaser Professional Solid Ink Transparencies, Phaser Weatherproof Paper, Phaser Postcards,Phaser Trifold Brochures. Media sizes: A/Letter, Legal, Executive, Statement, US Folio, A4, B5 JIS, B5 ISO; Envelopes: #10 Commercial, DL, and C5.
Tray 3: 525-sheet Feeder (standard on DX) Same media weights and sizes as Tray 2.
Tray 4: 525-sheet Feeder (optional) Same media weights and sizes as Tray 2.

Go the "print" dialog and select "settings". Ensure that the paper size, margins and orientation are not set for 8.5x11.  You did not mention the software you are using to print the envelopes/labels so this is the only guess I can give.   I have seen software that made me have to override the settings before.