DNS Certification Authority Authorization (CAA) uses your DNS records to let you specify which certificate authorities are allowed to issue certificates for the domains you own.
To test your domain, enter it below.
✔ All looks good
0 issuewild ";"
0 issue "letsencrypt.org"
0 iodef "mailto:firstname.lastname@example.org"
Check out sslmate for generating your DNS CAA records.
Then SSL Labs for testing your complete SSL config.