[exim] Received TLS cert status response, itself unverifiabl…

I setup a new server (OK, several months back) it is an Exim server, the
machines sole purpose is to send/receive mail.

I never fully put it into production because I see these strange errors in
the logs sometimes:

Received TLS cert status response, itself unverifiable

It seems to occur when sending mail to some remote hosts.... but not all.
A lot of traffic goes out using TLS and there is no issue.

When I get this error it occurs before the message it sent. It will
actually show the message as being sent using TLS successfully. Here is a
little snippet.

2015-11-24 07:09:32 1a17jH-0005wb-FR Received TLS cert status response,
itself unverifiable
2015-11-24 07:09:33 1a17jH-0005wb-FR => fvm@??? F=<
donotreply@???> R=ik_r T=r_smtp S=4299 H=mail.safe.com
[108.16.186.230] X=TLSv1:AES128-SHA:128 C="250 2.6.0 <1.0@???>
[InternalId=66884] Queued mail for delivery"
2015-11-24 07:09:33 1a17jH-0005wb-FR Completed

I did some Google searching, the only thing that shows up is Exim source
code in github.

I checked my other production servers and that error never occurs.

Any ideas?


Robert G.