I recently upgraded to Zimbra 8.7. We provide clients Authenticated SMTP relay, but several have older Outlook apps that are not sending a valid HELO in their connection. In 7.x versions of Zimbra, the mta would fix this on the fly by adding the server's hostname to the end of the client HELO. This has stopped in 8.7 and I have been trying to find a way to enable this behavior.
ESMTP helo=<Art> would become
ESMTP helo=<Art@server.example.com> so servers with strict HELO rules would not bounce with "Invalid HELO address"
Does anyone know a setting for this in Zimbra/Postfix?