In Thunderbird 52 a new behavior was introduced for replies to mailing list posts: "When replying to a mailing list, reply will be sent to address in From header ignoring Reply-to header". A new preference mail.override_list_reply_to allows to restore the previous behavior.
To unsubscribe from the LSTOWN-L list, click the following link:
http://peach.ease.lsoft.com/scripts/wa-PEACH.exe?SUBED1=LSTOWN-L&A=1