LISTSERV  accepts mail  in RFC822  format,  CMS NOTE  format, and  "PROFS
format" (I don't run OV and have  no idea what this means to OV exactly).
Mail in RFC822  format (filetype MAIL, or NOTE with  the first line being
'Received:') must have valid RFC822 fields. Using AT rather than @ is not
allowed and LISTSERV must  not accept it. I don't know  the status of PEM
but I see two possibilities:
 
1. IBM thinks it is delivering in  RFC822 format but uses AT. Complain to
   IBM until they fix it.
 
2. IBM doesn't think  it is delivering in RFC822 format.  In that case it
   should not have the  filetype MAIL. You can't report this  to IBM as a
   bug because IBM doesn't have  any native support/definition of RFC822.
   IBM  is free  to say  that filetype  MAIL corresponds  to OV  and that
   RFC822 has filetype XYZ, and we can't do anything about it. However, a
   community of hundreds of networked  IBM customers have been using MAIL
   as an indicator of RFC822 format for  over a decade and this cannot be
   changed. It's  up to  IBM whether  they want to  make life  easier for
   these customers.
 
  Eric