I was going through message tracking, external user may not be receiving emails from us, and I ran into these two errors I had not seen before, Hard Direct Fail and No Suitable Shadow Servers.

the email in question is being forwarded from an AS400 through our Exchange 2013 through a relay connector, also we have two Exchange 2013 servers and a witness server to form a DAG group.

does the shadow server refer to the 2nd exchange in the DAG group?

I ran several status checks on the DAG group, and status appears to be ok.