Can't proxyauth to cyrus imap (BAD Unrecognized command)

Hi,

i am trying to use imapsync-1.882 (first time using this tool) to sync Mailboxes from a very old Cyrus imap-server (2.1.18) to a modern version of docevot. I never used proxyauth before. I added the admin User to the Cyrus Conf:

# grep tt-admin /etc/imapd.conf
admins: root adminuser
proxyservers: cyrus adminuser

I want to sync E-Mails from syncmepls to foo@example.com on host2 (localhost where imapsync is running). This is what i use to sync:

./imapsync --host1 x.x.x.x --tls1 --user1 syncmepls --authuser1 adminuser --proxyauth1 --password1 MASKED --host2 localhost --tls2 --user2 foo@example.com --password2 MASKED --dry

Host1: will try to use PLAIN authentication on host1
Host2: will try to use LOGIN authentication on host2
Host1: IMAP server [x.x.x.x] port [143] user [syncmepls]
Host2: IMAP server [localhost] port [143] user [foo@example.com]
Host1: connecting and login on host1 [x.x.x.x] port [143] with user [syncmepls]
Host1 IP address: x.x.x.x
Host1 banner: * OK mx5 Cyrus IMAP4 v2.1.18-IPv6-Debian-2.1.18-1 server ready
Host1 capability before authentication: IMAP4 IMAP4rev1 ACL QUOTA LITERAL+ MAILBOX-REFERRALS NAMESPACE UIDPLUS ID NO_ATOMIC_RENAME UNSELECT CHILDREN MULTIAPPEND SORT THREAD=ORDEREDSUBJECT THREAD=REFERENCES IDLE STARTTLS ANNOTATEMORE
Host1: Socket successfuly converted to SSL
Host1: x.x.x.x says it has NO CAPABILITY for AUTHENTICATE PLAIN
Host1: frequently PLAIN is only supported with SSL, try --ssl or --tls options
Host1 failure: Error doing proxyauth as user [syncmepls] on [x.x.x.x] using proxy-login as [adminuser]: 5 BAD Unrecognized command

Any help with this would be greatly appreciated.