On 2020-03-25 Hartmut W Sager wrote:
Say, Trevor, one unrelated peculiarity. On this reply to your MUUG RoundTable posting, just like on my initial reply last night, my "to" (and "cc") field only had your personal e-mail address, not the MUUG RoundTable address. This time I caught it before "send" and manually added the MUUG RoundTable address. Are you doing something unusual in your e-mail, like a jinxed "reply-to"?
The MUUG mailing list program, Mailman, is mostly responsible for those headers and whether reply-to goes to sender or list. It's a configurable option for us admins. However, just like you saw, I find that sometimes Mailman does weird things and sometimes just hitting reply will go to list and sometimes just to sender. I haven't seen much rhyme or reason for that yet.
Most MUAs (like what I use, clawsmail) has a separate reply-all and reply-sender buttons and I try to use those exclusively for muug list replies so I know precisely who it's going to without having to double-check the headers.
Maybe others more familiar with this header/mailman behavior can offer some guesses as to why mailman sometimes gets it right, and sometimes wrong.