MT, I feel your frustration. My SM does the same thing with emails to my DF (he's not on his own account, computer illiterate), letters, packages, and phone calls. She's made it clear from day one of their marriage that his kids were out and hers were in. He wasn't "allowed" to invite us out to dinner w/o her, so he'd tell us to be quiet about it. Sneaking around w/your own DF - kinda weird.
I think your DIL is doing a major power play, and unfortunately the only thing you can do is hope DS finds out somehow (if you blatantly tell him & DIL finds out you'll be cut off for sure) and that he steps up to demand uncensored access to his FOO. He needs his own account. It's hard to believe a young person these days uses his wife's email address and vice versa. He can get a free one easily that she can't access. (There's no hope for my DF, he's just not interested in learning how to email.)
I do take it personally when I'm treated that way by SM, and probably would if DIL screened DS's messages. In a free society that is not OK. And I don't think the effectiveness or ineffectiveness of passing on a hug or a kiss has anything to do with your DIL's refusal, I think she finds it distasteful to deal with you at all. Sorry to sound so harsh, but that's MHO. People say "give so-and-so a hug from me" all the time. It's a thing; most of us just say OK will do, whether we actually do or not, or whether or not we think it's "effective." We say OK to be polite to the giver, not necessarily the recipient.
