There are two ways to get printed envelopes.
You can print as ready a standard envelope, but then you have to consider with the print area and design limitation.
You can print on a sheet of paper and get envelope printed on both sides in pantone or in cmyk colour, and then from this sheet produce an envelope. In this case, no restrictions exist.
The most used printing technique is offset print, rarely – screen-printing, foil printing, relief printing. For special effects can be applied by UV varnishing.