I'm having the exact same issue: root@server1:~# doveadm sync -u username remote:server2 dsync-server: invalid option -- 'U' Error: doveadm: Unexpected or incomplete option: -U dsync-local(username)<DhyOCo4H2GhtOAcAMnEMxw>: Error: read(192.168.109.2) failed: EOF (version not received) dsync-local(username)<DhyOCo4H2GhtOAcAMnEMxw>: Error: cmd sync: Remote command returned error 64: ssh server2 doveadm dsync-server -uusername -U
Looks like doveadm sync is executing dsync-local on the remote server, while passing an unsupported -U command. This started happening when I upgraded my 1st server from 2.3. I reversed the replication direction, and convinced myself it was working, but after upgrading the last server, they can't replicate in either direction.
-- Pete Greening