Banner : * OK IMAP4 ready
Host host1 says it has NO CAPABILITY for AUTHENTICATE LOGIN Error login : [host1] with user [user1] auth [LOGIN]: 3 NO cleartext logins disabled.

My entry is :
imapsync --buffersize 8192000 --nosyncacls --subscribe --syncinternaldates --host1 oldserver --user1 user1 --password1 oldserverpassword --host2 host2 --user2 user1 --password2 zimbraserverpassword --noauthmd5