We had a serious mail loop going here last week between LISTSERV and a Novell Groupwise system in New York state, OSC.STATE.NY.US. Some user there had set up a vacation program that apparently responded to every message with one that said "I am on vacation until ..." and maybe a blank message for good measure. Somehow it got started on this with LISTSERV itself (rather than a list) and it continued because "I" is an abbreviation for the LISTSERV INFO command. As a result, the user was not served out after 20 invalid commands. Nothing was sent to the LISTSERV postmasters. By the time we discovered it, there were several thousand of these messages (and blank messages too) mixed in with valid files in LISTSERV's reader. I served out the address, so that LISTSERV would not reply, but they continued to come for almost a day, until we were able to contact the people responsible for the Groupwise system. Eric provided a change to LISTSERV to remove "I" as an abbreviation for "INFO". After we applied that change, LISTSERV stopped a very similar loop that was about to start with a completely different Groupwise system, but also involving a vacation message starting with "I". So the fix was very useful, but it still seems like LISTSERV's loop detection for command jobs could use some improvement, such as limiting the number of command jobs accepted from any one address in a day. It also seems like it would be a good idea to count an empty message as an error.