DCTL1025

use of underscore detected in a host: element

Template host parameter includes static underscore character, in host or domain name. This is not strictly speaking wrong or illegal, but one should stop and think if use of underscore is appropriate in the given context.

Fix: If the underscore is not part of a service record prefix (like _dmarc, _domainkey, etc.), consider removing it. Standard hostnames should use only letters, digits, and hyphens.

Why do you hate underscore so much? Answered by Paul Vixie in presence of Paul Mockapetris: https://www.youtube.com/watch?v=VcwQPK4GTMs&t=1345s TL;DR, underscore caused security vulnerability.

Notice that underscores are used as attribute leaves; https://www.rfc-editor.org/rfc/rfc8552.html