[Dovecot] Replication fails with "Remote dsync doesn't use compatible protocol"

[Rich Wales]

> richatwork dovecot: doveadm: Error: dsync-remote(richatwork): Error:
> dsync(local): Remote dsync doesn't use compatible protocol

I was finally able to get replication working by abandoning the "wrapper
script" approach and, instead, putting a "mail_replica" value on each line
of the userdb file -- like this:

richatwork:<hashed password
here>:5003:5003::/home/mail/richatwork::userdb_mail_replica=remote:richatwork at pigeon.richw.org

The root dsync public key in each individual account's .ssh/authorized_keys
file has a command= parameter invoking "/usr/bin/doveadm dsync-server" with
the appropriate "-u" option.  As I noted in an earlier e-mail, if you put a
command= parameter on a public key in the "authorized_keys" file, you don't
need to specify the command in the "ssh" command line -- in fact, there is
no point to doing that (any command in the "ssh" command line is ignored if
the public key on the target has a command= parameter).

Now that I have replication working, I have another question:

Is it sufficient to configure just one server for replication in order to
have changes propagated in both directions?  Or do I need to configure
replication on both servers (with each one replicating to the other)?

Rich Wales
richw at richw.org