FYI:

Brother printers mostly have good drivers for download from the Brother web site (not packed with the printer), but didn't work for envelopes as installed. For the HL-3170CDW color printer the driver defaults to "PDF" as the printer language. For envelopes, this didn't work, placing the return address block for an envelope in the upper left corner of a letter size page. This position falls off the area of a #10 envelope in the center of the machine, from the manual paper feed slot. Same result when selecting either landscape or portrait orientation. Envelopes print properly when the printer language is changed to PostScript at /file/print/, click on 'Properties' then on 'Device' tab. Then use the pull down menu 'Printer language type' to select 'PostScript (Level from driver)'. Also select 'Landscape' orientation and 'Com-10' for the paper type (that's the #10 envelope). This feels too complex but simplification for the user would seem to require an 'envelope sensor' in the printer.