[Dovecot] Migration between namespaces breaks outlook on mac's

[Mark Zealey]

Hi there,

We're running dovecot 1.1 on one set of servers with a courier-imap-like 
namespace configuration:

namespace private {
     separator = .
     prefix = INBOX.
     inbox = yes
}

We're now migrating customers onto a dovecot-2 platform, switching from 
Maildir to sdbox (using dsync mirror) & changing the namespace at the 
same time. New namespace configuration looks like (as taken from 
http://wiki2.dovecot.org/Namespaces)

# This is for courier-imap namespace compatability
namespace {
     type = private
     separator = /
     prefix =
     inbox = yes
}

namespace {
     type = private
     prefix = INBOX.
     separator = .
     inbox = no
     hidden = yes
     list = no
     alias_for =
}

For 99% of clients this works fine eg thunderbird on first login after 
migration notices the folder structure has changed & automagically 
redownloads folders & emails. However I have noticed some really strange 
messages in the logs which seems to be related to customers running 
outlook on macos. When they login after migration they are generating 
commands like:

dovecot: imap(xxxx): Mailbox created: INBOX 1 1 1 1 1
dovecot: imap(xxxx): Mailbox created: INBOX 1 1 1 1 1 1
dovecot: imap(xxxx): Mailbox created: INBOX 1 1 1 1 1 1 1
dovecot: imap(xxxx): Mailbox created: INBOX 1 1 1 1 1 1 1 1
dovecot: imap(xxxx): Mailbox created: INBOX 1 1 1 1 1 1 1 1 1
dovecot: imap(xxxx): Mailbox created: INBOX 1 1 1 1 1 1 1 1 1 1
dovecot: imap(xxxx): Mailbox created: INBOX 1 1 1 1 1 1 1 1 1 1 1
dovecot: imap(xxxx): Mailbox created: INBOX 1 1 1 1 1 1 1 1 1 1 1 1
...

this goes on a long time and we've not yet found a solution other than 
delete the imap config on their outlook and reconfigure. Does anyone 
have any idea why this might be happening, or if there is a way we can 
somehow have old namespaces for old customers, new namespaces for new 
customers (we are using sql login code so should be possible to do 
something like this in theory I think?)

Thanks,

Mark