I've done similar with a catch-all sub-domain for years. It does mean that my mail server sees a lot of junk activity as some email lists out there have many addresses in that sub-domain on them, but at least they are easy to filter out.

Some sites refuse to accept email addresses with more than one "." after the "@" but I figure if they don't understand email addresses I don't want to be trusting them with my details, even throw-away ones, anyway!

Unfortunately I was added to docusign by someone else who gave them my main address...