Do you mean RFC822 (the internal headers you see?) or the
SMTP RFC821 head called MAIL FROM?

   As far as I know a null SMTP MAIL FROM is still valid and
must be supported (but I admit I haven't kept up with the
latest RFCs so I'd appreciate an update if this has changed).
It is used in cases where the sender does NOT
want to get an error notification (e.g. output of a command
to LISTSERV).  But it should be owner-xxx  on mail from a
list iself.