I'm opening here a bug that was originally opened on kmail2 (Bug 292399). https://bugs.kde.org/show_bug.cgi?id=292399 Kmail 2 almost never shows attachment icons on IMAP accounts. Not clear whether the problem lies in kmail2 or the IMAP backend (see bug 292399 discussion). Many people would like to see this solved as it represents a major usability issue (it is impossible to filter emails according to whether they have an attachment or not). Reproducible: Always
I can reproduce the bug, or at least an interesting variant of it: If I receive an email with multipart/mixed, containing text/plain and a image/png on an IMAP server (MS exhange if that matters), then before it is automatically retrieved do a manual refresh (ctrl-L) to see the new message in the list, then the paperclip appears on the new email. If I do a refresh (ctrl-L) again the paperclip disappears. It never reappears.
I think this has the same cause as https://bugs.kde.org/show_bug.cgi?id=318108 and https://bugs.kde.org/show_bug.cgi?id=281853 I.e. your IMAP server doesn't support akonadi's $ATTACHMENT flag and therefore doesn't store it. So after a resynchronization it disappears.
The IMAP resource has a new maintainer, reassigning to him.
*** This bug has been marked as a duplicate of bug 291332 ***