LISTSERV uses a null return path (RFC821 MAIL FROM:<>) on its administrative mail, and some mail hosts reject this. I discard message with a null return path that do not match a few simple heuristics, so I lose things like subscription confirmations from services like JISCfail. This makes me cross.
L-Soft claim that LISTSERV is following the specifications, and they cite a couple of paragraphs from RFC 821 (published in 1982) and RFC 1123 (1989). However they fail to cite text from RFC 2821 (2001) which explicitly forbids what they are doing.
There are several types of notification messages which are required by existing and proposed standards to be sent with a null reverse path, namely non-delivery notifications, other kinds of Delivery Status Notifications (DSNs), and also Message Disposition Notifications (MDNs). [...]
All other types of messages (i.e., any message which is not required by a standards-track RFC to have a null reverse-path) SHOULD be sent with with a valid, non-null reverse-path.
The only other permitted use of null return paths that I know of is vacation notifications, described in RFC 3834 (published in 2004).
L-Soft needs to get a grip, read some RFCS, and fix their software.