[Dovecot] POP3 UIDLs with virtual INBOX and migration from maildir->mdbox

[Timo Sirainen]

On Thu, 2012-02-09 at 15:35 +0100, Peter Mogensen wrote:
> Hi,
> 
> Considering the scenario, where you have some old account with a 
> different POP3 UIDL format and you migrate them to dovecot.
> 
> So these old UIDLs would be saved to dovecot-uidlist.
> 
> At some later time you want to introduce a virtual POP3 INBOX like 
> described on:
> http://wiki.dovecot.org/Plugins/Virtual
> 
> So you decide to make the new UIDL format "%f" - to make them unique 
> across folders.
> 
> So far so good.

Assuming the messages are in the same order, so far so good.

> But then you decide to migrate to mdbox with all your old UIDLs.
> The docs says that saving old UIDLs is only supported in Maildir and 
> that %f is only supported in Maildir.
> 
> So is this at all possible?
> 
> Would pop3_uidl_format = %g solve this (except for the old legacy UIDL's) ?

%g and %f are equal with Maildir. And if you migrated with dsync from
maildir to mdbox, then all GUIDs and POP3 UIDLs are preserved. But test
it first!

The main potential problem is that although UIDLs are preserved, their
order isn't and POP3 clients don't like the order changing. With Maildir
uidlist you can reorder POP3 mails to different than IMAP mails, but
with mdbox you can't currently.