When a user has an email reminder for a user send an email from another non-current wiki, open the notifications popup on upper right corner, mark all as read is no effect and mark item as read is unavailable for these notifications, and the notification only displays the wiki name and general message, no message header, clicking on it does not have the effect of opening or marking as read.
The user has to go to the wiki and then use the popup to mark as read, or filter the wiki from all notifications page and mark each group as read for each email.