Last Call Review of draft-ietf-extra-imap-messagelimit-08
review-ietf-extra-imap-messagelimit-08-artart-lc-leiba-2024-03-13-00

General comment:  It seems very odd for this to apply to EXPUNGE.  First, the
overhead in expunging is low.  Second, the client has no control over the
number of messages that will be expunged, as it just has to do with which
messages happen to have the /Deleted flag set on the server, and having a limit
on UID EXPUNGE and not on EXPUNGE would be strange and hard to justify.

— Section 3.1 —

   If a server implementation doesn't allow more than <N> messages to be
   operated on by a single COPY/UID COPY command, it MUST fail the
   command by returning a tagged NO response with the MESSAGELIMIT
   response code defined below.

I think this needs to be clearer that the entire command is failed and that
*no* messages are copied.  It should not just rely on the example later in the
section to convey that.

   When IMAP MULTIAPPEND [RFC3502] extension is also supported by the
   server, the message limit also applies to the APPEND command.

Is that really all you want to say about using this with APPEND?  I think that
leaves it underspecified.  How is a partial result handled?  Tagged OK with
partial result?  Tagged NO with complete failure of the command?  And how about
including an example?

— Section 3.5 —

You are now making it permissible for servers to break compatibility with
clients that don’t support this new extension; that seems troubling.  I
understand that possibly servers are already doing that, but it seems bad to
define an extension that says it’s OK… basically, if you implement this
extension, you are abandoning older clients.

It would seem better to have the section talk about the i portance of
maintaining compatibility with clients that don’t support this extension, and
raise the possibility of abandoning compatibility only if it’s absolutely
necessary.

For example, one might suggest tolerance of the situation to some extent,
allowing older clients to exceed the message limit to a point in order to stay
compatible, but recognizing the need to stop when it’s excessive.  Maybe if the
limit is 1000 you still accept up to 5000 from a non-compliant client before
you give up, or something like that.

This is especially true for flag searches, for which much greater tolerance is
probably acceptable.  Maybe true for STORE as well.