Considerations when you create an Envelope layout
Because FileMaker Pro considers the selected printer and print or page setup information when it calculates margins and other measurements on the layout, you must verify these settings before you create an Envelope layout.
1.
Choose File menu > Print Setup (Windows) or Page Setup (Mac OS).
In Preview mode, you can also click Print Setup (Windows) or Page Setup (Mac OS) in the status toolbar.
2.
Also, if you feed the envelopes into the printer short-side first, choose a landscape (horizontal) paper orientation.
3.
Click OK.
After you create the layout, you might need to adjust the layout depending on the way you insert envelopes into your printer.
 
Manually feed envelopes into a center-feed printer
Manually feed envelopes into a left edge-feed printer
Keep the header and adjust it, as necessary, to match the printing to the envelope size. (A good rule of thumb for the header size is to subtract the envelope height from 8.5 inches.)
Manually feed envelopes into a right edge-feed printer
Note  FileMaker Pro uses merge fields when you create an Envelope layout. You can't enter or edit data using merge fields; switch to Table View (in Browse mode, click Table View in the layout bar), or use another layout for that purpose.
Related topics 
Creating a layout