Issue with exim and auth protocol

Hi,

I'm trying to set up exim (4.83) as a submission server, and need to set up the dovecot authentication in exim. I'm having an issue with that (documented at https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=756258)

The problem is that exim doesn't follow the handshake as described here: http://wiki2.dovecot.org/Design/AuthProtocol. The wiki page says that the client should start the handshake, but exim waits for the server to start and to receive the DONE command until it starts its own handshake.

What I actually get is:

exim connects to dovecot auth
dovecot    VERSION    1    1
dovecot    SPID    48

And then, dovecot stops (I presume it waits for the client handshake, VERSION and CPID). Exim on its side waits for the DONE. This results in the SMTP connection by exim never replying to the AUTH PLAIN command.

This is exim 4.80 (or 4.83) and dovecot 2.1.7.

I have another server set up almost exactly the same (but with dovecot 2.1.17) where it does work. In that case, dovecot finishes the handshake before exim starts its handshake. It results in:

exim connects to dovecot auth
dovecot    VERSION    1    1
dovecot    MECH    PLAIN    plaintext
dovecot    SPID    10905
dovecot    CUID    1
dovecot    COOKIE    d3861d29441f06d962490eab8549fd46
dovecot    DONE
exim    VERSION    1    0
exim    CPID    10619
exim    AUTH    1    PLAIN    service=smtp    secured

rip=82.247.184.53 lip=80.67.179.36 nologin resp=<base64 encoded string>

I don't understand what could change the dovecot behaviour in that regard. Is there a solution that would only require modifying the configuration?

Thank you,

Mildred