Although RFC822 does provide a way to quote any 7-bit character,
my experience is that very many MTAs and UAs out there cannot
be trusted to handle RFC 822 quoting properly. I've certainly
seen problems with addresses of the form
"BITNET%\"USER(_at_)NODE\""@relay-host.internet.domain
which, while perfectly legal in 822, is unlikely in practice to
make it from end-to-end without being modified.
If quoting doesn't work reliably in addresses, I don't see why
it would work in the phrase preceeding an address.
Keith