Assuming that the one message is sent to both lists in the same MUA at the same time

to: list-a, list-b


The sender's message has a (generated) quasi unique message id.  E.g., your message to this list:

Message-ID:  <[log in to unmask]>

Some receiver mail systems will only display (or perhaps catalog) ONE message when there are
duplicated messagei-ids.

/Pete

############################

To unsubscribe from the LSTSRV-L list:
write to: mailto:[log in to unmask]
or click the following link:
http://peach.ease.lsoft.com/scripts/wa.exe?SUBED1=LSTSRV-L&A=1