Symptoms
When adding an A record that includes an underscore symbol '_' in Plesk at Domains >example.com> Hosting &
DNS > DNS Settings, the following message appears:
The specified domain name is not valid. You need to specify a valid domain name like domain .com
Cause
Underscore characters ("_") are not permitted in non-TXT DNS records created in Plesk. Having one or
more such records in a DNS zone hosted in Plesk causes bind DNS server fail to start.
This behavior will be improved in scope of PPPM-11448 i future produce updates..
Resolution
Underscores can be used with CNAME, SRV, TXT, DS records.
As a workaround, create a CNAME record instead of an A record.