It's related to the type of header: SHORTHDR vs SHORTBSMTP. The HDR
variants have spelled out 'To:' fields, the BSMTP variants have the
generic field. The default for BITNET addresses is HDR since the cost of
doing that is fairly low, given DISTRIBUTE and all that. The default for
Internet addresses is BSMTP since you'd kill your SMTP server in no time
otherwise. But if for any reason it is important to you to have your name
in the 'To:' field, you can switch between the options.
Eric