Issues with status 5.1.64 & 5.1.10

[PeterHagen]

I have an issue with status codes 5.1.64 & 5.1.10, which seem to be Outlook.com / Exchange specific. I couldn't find them in the RFC. So, the question is, should (and could) they be added to the statusCodes? As example:

{ 110, "not found by SMTP address lookup" },
{ 764, "TenantAttribution; Relay Access Denied"}