I am flooded by stupid "Mailbox is full" messages from Banyan and CC-mail gateways.

I suggest forwarding each and every one to the tech-support address at Banyan or at CCMail. If that doesn't work, send them to the president of each company, until they fix their products to adhere to Internet standards for where to send bounce messages. You have to keep pushing each problem back to its source; that's the only way they get fixed. I had good luck at this with Microsoft; I reported their bogus Win95 email software that would, by default, insert gibberish at the bottom of each message, to their tech support folks. When that got no useful response, I forwarded a copy of the bug report to <billg@microsoft.com>, with a suggestion that having numerous gibberish messages appearing daily in popular mailing list was making Microsoft look like unresponsive novices in the Internet market. Hmm, the problem went away... John Gilmore postmaster@toad.com