[Blind-sysadmins] Replied Emails going to sender.

Hi list does anyone know why when I reply to a message on this list that the original senders email is in the To field, rather than the blind sysadmins address. I keep forgetting so my apologies if people have received replies to their own email address. it never used to do this and does not happen on any other mailing list. Using thunderbird as my email client. Darren.