Envelopes are something my customers are always asking for and unfortunately the Japanese are very conservative as to what types of media they will support through their machines.
To cut a long story short, we have been setting up our customers for some years with envelope printing from both bypass tray and cassettes.
This can be done in two ways.
Method one. (late model machines only)
Measure the width and length of the envelope and create a "Custom paper" size in the others tab of the driver. Take note of the orientation as the width is measured left to right, ie feed direction. Also note, the envelope must be fed short edge so that it will pass through the feed rollers successfully which rules out the use of the Office "lable and envelope wizard."
You will need to create a matching page size in Word and when you print you select this page size from both the "original paper size" and "print paper size" drop downs in the properties tab.
For older machines that do not support "Custom paper size" you will need to select a page size that most closely matches the envelope width and chose that page size in Word and set the margins so the printing is virtually in the centre of the document. For a size 10 envelope I have used B4 size as the copier will accept this width in the feed direction as being "close enough" so will not trigger a jam. The newer series are certainly easier to set up and give less creasing throught the fuser, so if you really want to print envelopes, go for a new Masherbrum series. They are just sensational.
If your tech is persistent he or she will find the answer for you.
Good luck