When I go to the mailing list archive single-email, the drop-down that lets me choose other emails in the thread has a couple short-comings.
One is that the icon which indicates that the email has an attachment is using the "empty-page" icon which generally indicates creation of something new, not the "paperclip" icon which indicates an attachment.
Second, the presence of that icon messes up the level of indentation used to indicate which emails are responses to which other emails. Perhaps an all-white icon should be included in the front of all unadorned messages, to keep the indentation correct.