I have a subscriber that is not receiving anything, command responses or
posts, and I suspect that his ISP is filtering on a null "From ".

There are two commands that you can send to listserv, one will put a
null "From " and the other a non-null value.

Could someone please refresh my memory of which they are so I can test
my hypothesis?

--
Rich Greenberg   Work:  Rich.Greenberg atsign worldspan.com  + 1 770 563 6656
N6LRT   Marietta, GA, USA   Play: richgr atsign panix.com    + 1 770 321 6507
Eastern time zone.   I speak for myself & my dogs only.     VM'er since CP-67
Canines:Val(Chinook,CGC,TT), Red & Shasta(Husky,(RIP))        Owner:Chinook-L
Atlanta Siberian Husky Rescue. www.panix.com/~richgr/   Asst Owner:Sibernet-L