Unable to install Let's Encrypt: SERVFAIL looking up CAA for example.com

Symptoms

1. Unable to install Let's Encrypt extension:

   PLESK_ERROR: DNS Problem: SERVFAIL looking up CAA for example.com

2. External name server is specified in Domains > example.com > DNS Settings.

Cause

Plesk Onyx 17.0 or 17.5 does not support CAA. Since CAA is missing, the external server returns error.

Resolution

1. Determine the SOA server for the domain:

   # dig SOA @8.8.8.8 example.com +short
   ns1.exampleproviderserver.com. support\@exampleproviderserver.com. 17 900 600 86400 3600

2. Contact the external name server owners to clarify why SERVFAIL error is returned. Normally, when a record like CAA is missing for domain, name servers return "no record" instead of SERVFAIL. 

   Note: CAA DNS records are supported in Plesk 17.8

   Note: the issue may be temporary. Try to issue the certificate once again in an hour.