The date-time the email address was created (immutable; server-set).
The name of the client that created this email address (immutable; server-set).
The email address (immutable; server-set).
The id of the masked email address (immutable; server-set).
The date-time the most recent message was received at this email address, if any (server-set).
Immutable, server-set properties for MaskedEmail objects