http://wiki2.dovecot.org/Variables states that %w only works for Dovecot-auth so this does not seem to work for imap client proxy. I read that, yes. However I didn't know how this works, but I expected dovecot-auth (whatever that may be) to perform the authentication to the old mailserver, so I thought: "I guess %w must be available then..."
Anyway, thanks for pointing that out.
I assume you will need to use a master user (masteruser) to login on behalf of the actual user (loginuser), since the user should be already authenticated when he sees the namespace "oldmail". Yep, I have just tried that approach, and it works fine. Thanks!
There is just one thing left to sort out: From the moment we have migrated to dovecot, new accounts will not be (manually) created anymore on our old server, meaning: more and more mailboxes will become unavailable on the old server.
It seems (but I have not yet done a lot of testing) that if the imapc cannot 'mount' the old mailbox, the imap process 'dies'. (that's what squirrelmail tells me)
Since you know so much... :-) Do you happen to know a way to make the imapc non-mandatory..? Like: when 'mounting' fails: simply ignore it, and proceed as normal.
Thanks very much for you kind assistance!
Mourik Jan