[Pkg-exim4-users] Two Message-ID headers - filter out to only one?

[Bruce A. Bergman]

Hello esteemed colleagues! :)

I have a slight issue I thought I would ask about. My exim4 server is 
running great, and has been for some time. On that same server, I have a 
WordPress website plugin that occasionally sends out an email 
notification to users. When it does so, it seems to insert its own 
Message-ID header, and that results in two Message-ID headers in the 
outgoing message. Some remote mailers will allow that, but many do not. 
I typically get:

     SMTP error from remote mail server after end of data:
     host eforwardxxx.registrar-servers.com [...]:
     550 Messages should have one or no Message-ID headers, not 2.

Looking at the outgoing message, I see:

    Message-ID: <6a6f578b3e36ac79970664a958f99a57 at www.example.com>  <-- 
presumably generated by exim4
    [...]
    Message-Id: <20140829202747.39484800 at www.example.com>  <-- WordPress 
plugin generated

Is there any rule I can insert that would take one of the Message-ID 
headers out of a message before it is sent on? I don't think it really 
matters which one is kept... This isn't a big deal; it's really more of 
an annoyance than anything, but if I could nix it, I'd be happy. :)

Thanks!
bruce