Dns Domain Name Underscore. It is completely valid to have an underscore. While a hostname may not contain other characters such as the underscore character _ other DNS names may contain the underscore.
The DNS names of all the nodes that require name resolution include the Internet DNS domain name for the organization. For these use cases renaming the hostnames may be your only solution. While a hostname may not contain other characters such as the underscore character _ other DNS names may contain the underscore.
In DNS host names are the name fields of A or MX records or the data fields of the SOA and NS records.
This restriction was lifted by RFC 2181. Underscores have special use in DNS. Underscores allowed except in host names. Domain_namelocal הקו התחתי קיים גם בשם netbios וגם בשם dns הפנימי של הרשת וזה ימנע ממני.