Retrieving mail from read-only mdbox

[Mark Moseley]

This is a 'has anyone run into this and solved it' post. And yes, I've been
reading and re-reading TFM but without luck. The background is that I'm
working on tooling before we start a mass maildir->mdbox conversion. One of
those tools is recovering mail from backups (easy as pie with maildir).

We've got all of our email on Netapp file servers. They have nice
snapshotting but the snapshots are, of course, readonly.

My question: is there a doveadm command that will allow for email to be
retrieved from a readonly mdbox, either directly (like manipulating the
mdbox files directly) or by doveadm talking to the dovecot processes?

Ideally, there'd be something like doveadm dump, but that could dump
selected message contents.

I've tried using IMAP with mail_location pointed at the snapshot, but,
though I can get a listing of emails in the mailbox, the fetch fails when
dovecot can't write-lock dovecot.index.log.

If anyone has gotten something similar to work, I'd love to hear about it.
A working IMAP setup would be the ideal, since it's more easily automatible
(but I'll take whatever I can get).

Any and all hints are most welcome!