Require "urn:ietf:params:jmap:mail" capability when calling MDN/set?

[cketti]

This is similar to #311.

We could require MDN/set to add the "urn:ietf:params:jmap:mail" capability in the using property of the request because of the implicit call to Email/set. Failing to provide the capability would return a unknownMethod error response for the implicit call.

However, using this approach could allow a client to send multiple MDNs because the $MDNSent keyword isn't added to the message and that keyword is used as rejection criterion by the server.

If this is unwanted behavior, I see the following two options to forbid it:

• require both capabilities for the MDN/set call, i.e. MDN/set will fail when the "urn:ietf:params:jmap:mail" capability is missing; not only the Email/set call
• make the "urn:ietf:params:jmap:mail" capability implicit, so we can't run into an unknownMethod error

[rouazana]

Thanks, I addressed this point here: f953dd3#diff-a85095bca98d6fb8b1e3df07858d7f47R75