Added criteria for valid MX domain record name and target entries

Author: bbiggerr

openapi.yaml

@@ -20732,7 +20732,11 @@ components:
             `NS`: The subdomain, if any, to use with the Domain of the Record. Wildcard NS records (`*`) are not supported.
 
             `MX`: The mail subdomain. For example, `sub` for the address `[email protected]` under the `example.com`
-            Domain. Must be an empty string (`""`) for a Null MX Record.
+            Domain.
+            * Must have less than 256 total characters.
+            * The left-most subdomain component may be an asterix (`*`) to designate a wildcard subdomain.
+            * Other subdomain components must only contain letters, digits, and hyphens, start with a letter, end with a letter or digit, and contain less than 64 characters.
+            * Must be an empty string (`""`) for a Null MX Record.
 
             `CNAME`: The hostname. Must be unique. Required.
 
@@ -20759,10 +20763,11 @@ components:
 
             `NS`: The name server. Must be a valid domain. Required.
 
-            `MX`: The mail server. Must be a valid domain unless creating a Null MX Record. To create a
-            [Null MX Record](https://datatracker.ietf.org/doc/html/rfc7505), first
-            [remove](/docs/api/domains/#domain-record-delete) any additional MX records, create an MX record with empty strings
-            (`""`) for the `target` and `name`. If a Domain has a Null MX record, new MX records cannot be created. Required.
+            `MX`: The mail server. Must be a valid domain unless creating a Null MX Record. Required.
+            * Must have less than 256 total characters.
+            * The left-most domain component may be an asterix (`*`) to designate a wildcard domain.
+            * Other domain components must only contain letters, digits, and hyphens, start with a letter, end with a letter or digit, and contain less than 64 characters.
+            * To create a [Null MX Record](https://datatracker.ietf.org/doc/html/rfc7505), first [remove](/docs/api/domains/#domain-record-delete) any additional MX records, then create an MX record with empty strings (`""`) for the `target` and `name`. If a Domain has a Null MX record, new MX records cannot be created.
 
             `CNAME`: The alias. Must be a valid domain. Required.