fd6cdfac_ate__RA_API____Dyn_Help_Center__Description
[Field] mx [Additional Info] The specified MX must resolve to an IP address, or it will be ignored. Specifying an MX of NOCHG will cause the existing MX setting to be preserved in whatever state it was previously updated via a client or the Dyn website. Parameter is ignored for Dyn Standard DNS hosts. [Description] 
Specifies an eMail eXchanger for use with the hostname being modified. (Deprecated: Flag is currently ignored)
Perform Update (RA-API) | Dyn Help Center
Description