I'm sharing an IMAP mailbox with another person. So we both have IMAP clients, in order to read mail messages and post some.
However, when I read a message, its state is set to "seen" (or "read"), usually by flagging it. But, I also want the other person to notice this message as "unread" (or "unseen"), so I change its state to "unread".
This policy of reading the mail is less than optimal.
Is there an extension to IMAP so that a message could have the extra "meta-data" of "read by user x"? I think it's possible by flagging the message, but it also needs the IMAP client GUI to implement this.