Most computers will print envelopes, but you need to put it on a different setting, especially for heavier envelopes. (The fuzziness is the photograph, not the printing!) In my printer Canon Pixma IP4500, you go to printing, properties and media type, then select envelopes.
I was delighted that these envelopes printed so beautifully on a matt metallic paper. I then wrote the names by hand in gouache.
Some people print labels then stick them onto the envelopes. this is such a pity when it is a lovely quality envelope for something like a wedding.
I like my envelope layout to always work as follows: I have the horizontal base line for the name to be halfway down. I only move it up if the address is really long. When I use a printer I centre the address because it always looks comfortable, whereas if you left align it, some of the addresses won’t fit as well as others.
I’ll talk about hand-addressing in calligraphy en masse in due course – maybe tomorrow!