I use sticky tape. Like Scor tape or the red liner tape. For the sealing part of the envelope there is an envelope glue that you can buy and you put it on and let it dry and then when you want to use it you just went the glue like you would lick the envelope to seal. There are threads about making your own glue, but I just use the double sided sticky tape. I put a piece on and then when I am ready to mail, I just peel off the shiny side and it works just as well.
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