The domain segment must only contain the following characters

Nov 23, 2018
13
3
3
Denmark
cPanel Access Level
Root Administrator
Cannot add server with _ in the beginning eg: _spf.google.com
Using the the new UI manager for Email Deliverability: Manage > SPF > Additional MX Servers(or Additional Host)
String mask not allowing underscore.

I mentioned this during a support session, but not sure it was noted.