If you are saying you used your mail program to send directly to that address then this is NOT a Nabble Support issue (which is what I thought originally given the strange error message).
Nabble is only responsible for getting the archive to work. It has no direct involvement with the mail list itself.
I have no suggestions about how to contact the mail list owner. The address you used is likely to be the appropriate one to use.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.