A reply to my first posting about X- records.
 
----------------------------Original message----------------------------
X-anything is supposed to be ignored, basically.  If you have some peculiar
function you want to implement on your UA/MTA, you can look for particular
X-tags.  Listserv generates the X-To's when the original mail is sent to
other recipients other than the list name.  Listserv also communicates
between peers using X-tags in the headers.  X-tags are passed in transit, but
are only meaningful to specific UAs/MTAs.
 
/Jeff/