TLS negotiation fails

[Walter Ian Kaye]

I migrated (mostly) to a new server in AWS EC2 VPC running FreeBSD 
10.3 and installed the latest Qpopper.

I set up my .pem files (first I tried self-signed; now I'm using 
Let's Encrypt) but I'm getting error 20, unable to get local issuer 
certificate.

I hear the general advice that a CA root file needs to be referenced, 
but I don't see any options for that in the config file, so I'm lost.


Help?