[Smokin' Joe]

I haven’t put a return address on an envelope since I found out about “closed cover” monitoring in the 1970’s.

If it is tax deductible, yes. Otherwise, no. If anything, put the address you are sending the mail to in the return spot, in case the handling equipment shucks the stamps off (has happened to me numerous times).

[Buckeye McFrog]

If anything, put the address you are sending the mail to in the return spot,

Ahhhh....the old Free Franking Privileges scam. Put the recipient's address in the Return Address spot, put yours in the "to" spot, throw it in the mail with no postage and it gets "returned" to your recipient. I believe that one originated with Abby Hoffman in Steal This Book