A mail.cnx.email CNAME (-> mx1.cnx.email) lets clients (Thunderbird etc.)
use a friendly hostname for submission/IMAP. To avoid a TLS name
mismatch the cert now carries mail.cnx.email as a SAN, so the acme_mx1
key is authorized to write _acme-challenge.mail too. The MX still points
at mx1.cnx.email and --reuse-key keeps the DANE TLSA digest valid across
the re-issue.
Berwn
1dd3aadb97