The document extends the Sieve Email Filtering Language [RFC5228] by providing a number of action commands, some of which can generate additional messages of behalf of the user. It is a clear document, its target being developers and users of the protocol. I liked the fact that the authors included a 'Compatibility with Other Actions' section that describes the interoperability with existing deployed versions of the protocol, as well as the inclusion of a temporary section about Implementation Status. I am missing however some information about possible impact of the new action commands on deployment and operations on servers already in operation. I assume that scalability and compatibility between older and newer versions (including or not the new defined commands) were assessed, but this is not documented. Some confirmation, warnings (if any) and useful information that operators should know at deployment would be useful. I suggest that you consider adding such a paragraph or short section.