Barry Warsaw writes:
But maybe the OP has a different use case in mind and we could have a need for both a long-term, permanently failing retired lists, and shorter term, temporarily failing disabled lists.
I don't really understand under what circumstances a list owner would want to disable the *whole list* and at the same time leave retries up to arbitrary MTAs out on the Internet. The poster may or may not get a DSN. Etc, etc.
OTOH, I can imagine that for some purposes you might want a different status code, and I don't see any good reason for making that configurable and then restricting it to 5xx. Rather, document it as "this SHOULD be a 5xx code (in the RFC 2119 sense, ie, with sufficient reason it could be a 4xx code, but we don't know of any examples offhand :-)."