I received this error at the end of a migration from imapc to mdbox. Is it because I wanted doveadm 'sync' instead of 'backup'? I didn't get time to do any testing, but since you're pushing for the release, here it is:

kerio2:~ adminuser$ /opt/dovecot/bin/doveadm -o imapc_user=jsample -o imapc_password=****** -o imapc_host=*.*.*.* sync -R -u jsample_dc@mydomain.com imapc:/tmp/imapc dsync(jsample_dc@mydomain.com): Error: Can't update mailbox Archives/2011: Not supported dsync(jsample_dc@mydomain.com): Error: Can't update mailbox Archives/2012: Not supported dsync(jsample_dc@mydomain.com): Error: Can't update mailbox INBOX: Not supported

...etc, for all mailboxes in the account.

This is my userdb entry:

jsample_dc@mydomain.com:{***}password:502:6:IMAPC RECIPIENT::/bin/false:

kerio2:~ adminuser$ /opt/dovecot/bin/doveconf -n # 2.1.rc6: /opt/dovecot-2.1.rc6/etc/dovecot/dovecot.conf # OS: Darwin 9.8.0 Power Macintosh auth_cache_negative_ttl = 0 auth_cache_size = 1 M auth_debug = yes auth_mechanisms = plain login auth_username_format = %n@mydomain.com auth_verbose = yes disable_plaintext_auth = no instance_name = dovecot-2.1.rc6 listen = 192.168.20.40 mail_home = /var/mail/%d/%n mail_location = mdbox:~/mdbox mail_plugin_dir = /opt/dovecot/lib/dovecot mail_plugins = fts fts_squat # I know, this is deprecated in 2.1 mail_privileged_group = mail maildir_very_dirty_syncs = yes namespace inbox { inbox = yes location = mailbox Drafts { special_use = \Drafts } mailbox Junk { special_use = \Junk } mailbox Sent { special_use = \Sent } mailbox "Sent Messages" { special_use = \Sent } mailbox Trash { special_use = \Trash } prefix = } passdb { args = scheme=CRYPT username_format=%u /opt/dovecot/etc/dovecot/users driver = passwd-file } plugin { fts = squat } postmaster_address = postmaster@mydomain.com protocols = imap lmtp service auth { unix_listener /var/spool/postfix/private/auth { group = _postfix mode = 0660 user = _postfix } unix_listener auth-userdb { group = mail mode = 0660 user = adminuser } } service imap { executable = imap postlogin } service lmtp { unix_listener /var/spool/postfix/private/dovecot-lmtp { group = _postfix mode = 0666 user = _postfix } } service postlogin { executable = script-login rawlog -t } service stats { fifo_listener stats-mail { mode = 00 } } ssl_ca =