of course envelopes can be recycled. i sometimes reuse envelopes, especially the larger ones, and stamps. many times the stamps have missed the print or mark from the post office and they're good as new. lucky me. lol
when we lived in cheshire envelopes were not able to be put in the recycle bin - they said it was because of the glue. Now we are in lincolnshire the council here say envelopes are fine to put into the recycle bin as long as the clear cellophane panel is removed. I guess it depends on your council's rules
Different councils use different recycling machines and some items can be recycled in certain areas but not in others.
I can't put plastic bags or shredded paper in my Paper and Plastic bin. Odd. You would think shredded paper would be easier to recycle then whole sheets but apparently if already shredded it jams up the works.