Is it possible to fax a multi-page document printed on Legal size paper on the MFC 420cn.

it seems that on your model you can only use legal size paper on tray 1 & 2, then you have to set the paper size.
here is a link to instructions for your model.
http://download.brother.com/welcome/doc002258/mfc9840_uk_usr_b.pdf

(YES ) it will scan the whole page.

The receiving fax must have legal size paper available and their machine set to auto reduction.

Ask if the ones sending are sending legal size, it may be using 2 sheets to get all from a legal size document.

This document explains the different results obtained when using or not using the Automatic Reduction (or Auto Reduction) Feature. The following issues usually result when the Automatic Reduction feature is not set correctly:

• Faxes printing too small
• Faxes printing on more than one page
• A blank page ejecting between each printed fax page

This feature can be turned ON (the default) or OFF from the Advanced Fax Features menu. The two main purposes of the Auto Reduction feature

• Fits a received fax page onto the paper size loaded in the paper tray and selected in the paper size setting of the Basic Fax Setup. For example; if letter size paper is loaded in the paper tray and selected in the fax settings and a legal size document is received, each page will be reduced and printed on one letter sized paper.
• Allows the addition of the fax header margin at the top of every printed fax without extending the fax onto another page. The fax header is printed at the top of every fax received with identifying information about the fax sender. Since this increases the overall page length, the page must be reduced to fit onto one page. Auto reduction slightly shrinks the fax as it is received so the entire page will print on one piece of paper even though a top margin is allowed for the fax header.

I've seen this before...

The machine is calling for legal sized paper and it thinks it has it in the paper tray. Check the back stop that is inside the paper tray. It should be a green guide that is closest to you if you pull the tray out. You may have to lift up a flap on the end. Make sure that the paper stop is on the correct paper size for what is in the tray. Hope this helps. Let me know if you need any more assistance.

If this helps you please rate it as Fixya!

I have a Brother MFC-8840Dn (full legal-size flatbed as well as document feeder). I use Windows XP Pro and a USB connection. I'm not sure my fix works with other Brother models or different Windows operating systems, but it's a way to start troubleshooting at least.

I've always been able to print legal-sized pages from word processing or spreadsheet programs and receive legal-sized faxes. But I never could make legal-sized photocopies or PDF scans. The image was always cut off at Letter size. The fix is a Brother Utility set-up setting:

*** Go to Start / All Programs / Brother / MFL-Pro Suite MFC 8840Dn / Scanner Utility. (This link may also be called something like Scanner Settings.)
*** At the "Maximum Scanning Size", select "Legal" instead of "Letter/A4".
*** Click OK and restart your PC for the new setting to take effect.

It's like magic -- I can now scan a full legal-sized PDF, whether on the flatbed or through the ADF. I also tried a compressed TIFF scan and it came out fine.

**** Make sure your software and/or Brother Control Center scanning configurations are set to Legal if that's what you want for the particular image scan. The Brother Utility setting simply enables the option of choosing the larger legal-sized paper, which then allows the full legal-sized image scan, You always have to set your software to make that choice, just as you would to make and print smaller images on Letter, A4, envelopes, etc. (NOTE: I always start scans through software on my PC, like Adobe Acrobat or PaperPort, and the Utility Setting fix is working fine. However, I just tried pressing the SCAN button on the front panel of the MFC itself with a legal-sized document on the flatbed and through the document feeder. I still got Letter-sized image scans. So, there must be another setting somewhere for starting scans directly from the MFC that I'll locate later.)

I was about to buy a different brand of scanner because of the frustration with legal-sized images. It's like having a new scanner now :) I hope this Utility Setting info helps you troubleshoot your legal-sized image problem.

pleas check the driver settings, maybe there is a setting fit to paper or something.

To answer more effectively - how is the printer connected to the iMac? Is it a USB connection, a printer cable, is the MFC 6800 connected to a print server, an AirPor, etc? A second question I have is if you are trying any kind of tricky printing such as manualduplex printing.

Also, a shot in the dark...Is the Auto Reduction set to on or off? To check:
1. Press MENU/SET, 2 (Fax), 1 (Setup Receive), then 4 (Auto Reduction).

2. Press the up or down navigation key (keys located above and below the
MENU/SET key) until the display shows "Reduction: ON?".

3. Press MENU/SET.

4. Press STOP/EXIT.

Another item to keep in mind:
You can use three sizes of paper for printing your faxes and
copies---letter, legal and A4. When you change the size of paper you ha
ve loaded in the Brother machine, you need to change the setting for the paper size so your Brother machine can fit the incoming
fax on the page. To set the Paper Size:

1. Press MENU/SET, 1 (General Setup), then 1 (Paper Size).

2. Press the up or down navigation key to select LETTER, LEGAL, or A4.

3. Press MENU/SET.

4. Press STOP/EXIT.

You have to go into the menu and change the setting to Legal.

here is the manual:

http://www.fixya.com/support/p202524-panasonic_panafax_uf_595_plain_paper/manual-7600/page-3