Subject: Can't delete messages PCPINE via IMAPD to SUN

From: [email-masked] (Mike Santangelo)
Date: 12 Mar 97 18:12:19 GMT

Since installing the security patch for IMAPD a week or so ago,
our PC PINE 3.95 users are having an odd problem.  When they delete
a message, the message gets deleted and in its place the following
message appears in the INBOX (/var/spool mailfile):

  From [email-masked] Wed Mar 12 13:10:00 1997
  Date: Wed, 12 Mar 1997 13:06:33 -0500 (EST)
  From: Mail System Internal Data <[email-masked]>
  Subject: DON'T DELETE THIS MESSAGE -- FOLDER INTERNAL DATA

  This text is part of the internal format of your mail folder, and is not
  a real message.  It is created automatically by the mail system software.
  If deleted, important folder data will be lost, and it will be re-created
  with the data reset to initial values.

What's going on here?
-- 
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Mike F. Santangelo, Dept. Head-Computer & Network Systems, UMCEES/CBL Solomons

---

From: Terry Gray <[email-masked]>
Date: Wed, 12 Mar 1997 23:22:49 -0800 (PST)

>   with the data reset to initial values.

Mike,
The "mystery message" is a feature of many IMAP4 servers that use standard
Unix mailbox format.  In your case, I'm guessing its appearance is
actually a side-effect of upgrading an IMAP server from IMAP2bis to IMAP4
level.  But it's only visible in specific situations.  In particular, it
should not be visible to PC-Pine users, or in any other IMAP clients. 

Unlike the earlier IMAP2bis specification, IMAP4 supports the concept of
unique message IDs that persist across sessions.  These can be used for,
among other things, folder resynchronization in disconnected operation. 
Recent versions of POP have a similar concept (UIDL).  The IMAP4 UID info
has to persist across sessions, and part of it relates to an entire
mailbox, rather than an individual message.  Soooo, where to store it?  In
the case of the normal Unix mailbox format, that's a problem.  Answer: put
a "fake" message at the beginning of the mailbox, and put the necessary
info somewhere in that message. 

Here are the key points:

 o Some mailbox formats provide other places to put this info, but the
   normal Unix mailbox format doesn't provide many options; hence, the
   mystery msg at the beginning of the mailbox.

 o Mail clients accessing the mailstore via IMAP or POP will never see it,
   assuming the IMAP and POP servers share the same discipline.

 o Mail clients that directly access the mailstore (local disk or via NFS)
   *will* see it and display it, unless they have been taught to ignore
   it.

 o Deleting the message won't help... it will just come back again.

 o Pine 4.xx will not display it even when accessing the mail store
   locally, (and Pine 4 will be bundled with an IMAP4rev1 server rather
   than the IMAP2bis server that is part of the current Pine
   distributions.) 

If (and only if) you have mail clients directly accessing a Unix-style
mailstore that is also exported via IMAP or POP, then you have a dilemma,
at least until Pine 4.00 is available, since users will probably find the
mystery msg disconcerting if it is displayed.  In general, using the
latest IMAP4 server is recommended, but in these cases it may be better to
continue using an IMAP2bis server for a bit longer.  (The IMAP2bis server
that is part of the new Pine 3.96 distribution has all known security
holes plugged, as does the UW IMAP4rev1 server in our IMAP toolkit
distribution. ) 

-teg