JMAP names a failed method call `"error"` (RFC 8620 §3.6.2). The send
paths (normal send, raw/S-MIME send and submit, iMIP reply, invitation
and cancellation) and Sieve validation tested for `"<Method>/error"`,
which never matches, so a refused Email/set or EmailSubmission/set
could be reported as sent.
A method error before the submission is created now fails the send.
One after it comes from the implicit onSuccessUpdateEmail /
onSuccessDestroyEmail call: the message has already left, so it is
reported as a filing warning, not as a failed send that would invite a
duplicate resend.
Search turned every failure, including a method error such as
`unsupportedFilter`, into an empty result that read as "No results
found". A failed Email/query now throws, which the search view shows as
an error and the "All folders" fan-out reports per account.
Linus Rath