I wrote this to the Tramp and Gnus mailing lists:

"imap-hash.el lets you treat an IMAP mailbox as a hash.	It lets you get
individual keys' headers and body data (keys are message UIDs) or map a
function across *all the messages in the mailbox*.  The function is only
called for those that match a given subject, but really I should be
using SEARCH.  So the library is not optimized for speed.  Also, it does
not handle invalid mailbox names gracefully yet.  Consider it an alpha
version.

I plan to eventually use imap-hash.el to store distributed Gnus data,
specifically the Gnus registry, the newsrc file, scoring files,
etc.

tramp-imap.el uses imap-hash.el to provide a Tramp interface to read and
write files as messages in an IMAP mailbox.  It's also an alpha version,
but it will at least let you (given a valid IMAP mailbox) read and write
directory contents.  It uses EPG (thanks to Daiki Ueno's help) to
encrypt the file contents when they are stored as messages."

I would like to put imap-hash.el in lisp/net/imap-hash.el if possible,
to support Gnus and Tramp from one location.  Is that OK?  It would make
my life easier and others can use the library if they wish.  See attached.

Thanks
Ted