secure lmtp connection between sendmail and cyrus

[Marcus Schopen]

Hi,

I'm looking for a secure and stable way to connect sendmail (8.14.4) and
cyrus (2.4.12) in case of both hosts not running on the same machine or
in the same local secure subnet.

What is a practical way? An openvpn (tcp or udp?) connection between
sendmail and cyrus and starting lmtpd with -a option at the tunnel's
end?

Or a LMTPs connection with LMTP_AUTH, but couldn't find any good example
configs how to configure sendmail to use LMTP_AUTH und TLS to talk to
cyrus.

Cheers
Marcus