[Dovecot] Problems with POP3 UIDL when migrating from MBOX to Maildir

[Jonas Olsson]

2006/2/12, Timo Sirainen <tss at iki.fi>:
> On Sun, 2006-02-12 at 16:20 +0100, Jonas Olsson wrote:
> > Questions:
> > ----------------
> >
> > How does Dovecot generate the POP3 UIDL?
>
> Using pop3_uidl_format. %v means UIDVALIDITY and %u means message UID.
> With maildir those are taken from dovecot-uidlist file.
>
> > Is there any workaround that I could use to make Dovecot generate a
> > consistent POP3 UIDL output, enabling a migration from MBOX to
> > Maildir, or am I stuck with using MBOX?
>
> You can convert your mails in a way that preserves the UIDVALIDITY and
> UIDs. In mboxes the UIDVALIDITY is stored in X-IMAPbase or X-IMAP header
> in the first mail in the mailbox. UIDs are stored in X-UID header for
> each mail.
>
> So what you'd need to do is create some script to build the
> dovecot-uidlist file properly. As far as I know no-one's done this yet,
> but it shouldn't be too difficult.
>
> dovecot-uidlist file format is:
>
> <uidvalidity> <next-unused-uid>
> <uid> <filename>
> <next uid> <next filename>
> ..
>
> You should also set next-unused-uid value properly. It's also in
> X-IMAPbase/X-IMAP header as the next number after UIDVALIDITY.

A quick lock through the current mailboxes reveals that 28 of them
contain messages but lack an X-IMAPbase/X-IMAP header. A large
majority of the mailboxes also lack any X-UID headers.

I can get the UIDVALIDITY base of the the mailboxes missing an X-IMAP
header by connecting to the Dovecot POP3 service, I guess, but how
about all the mailboxes lacking X-UID headers? Is there a way I can
determine, in a scriptable way, which message has which UID or should
I assume that the UIDs are assigned in chronological order based on
the next-UID value in the X-IMAP header? That is, the last message in
the MBOX file has UID = next-UID - 1, the next to last = next-UID - 2,
and so on?

Thank you for your replies by the way. They are very helpful in making
this migration happen.

--
/Jonas Olsson