[imp] Accounts with no INBOX

[R Phillips]

IMP version 5.0.14

We have some accounts here with the slightly atypical setup where they
don't have mailboxes but access shared mailboxes.  It arises from
needing accounts with an annual rotation of users but needing a
consistent contact point (eg society-president, the contact address has
an alias).  How this is relevant is that the mail account for the
username does not have an INBOX.  On it's own this would create the
"IMAP error: Mailbox does not exist" message, but with a shared mailbox
this produces a HTTP 500 error.

Subjectively for these long established accounts may also be responsible
for creating PHP "memory exhausted" errors based on some correlation of
logging information.

In my tests by setting up a test account, removing the INBOX and sharing
a mail folder I get the following:

PHP Fatal error:  Call to a member function url() on a non-object in
/path/to/horde/imp/lib/Imap/Tree.php on line 1614, referer:
https://webmail.bath.ac.uk/login.php


We used to run IMP successfully with these accounts (so I'm told) prior
to the pear packaged versions, and my last conversation with the mail
administrator here did touch on creating empty Inboxes to get around
this issue.

However, is this a setup you could see IMP being able to deal with in
the future?  Would it be better to not produce a HTTP 500 response in
this (admittedly slightly odd) circumstance?