dovecot + sieve: message recovery possible after rule pointed to invalid mailbox?

[dovecot at ptld.com]

> On 05-09-2022 11:05 am, Charles Gresham wrote:
> 1, Customer created a mailbox (aka subfolder) "ABC" and setup a Pigeonhole Sieve script to file the messages into it. So fine, so good. All seemed to work out
> well.
> 
> 2. Customer renamed the mailbox to, let's say, "CDE" and did not change the Sieve script
> accordingly.
> 
> 3. We noticed this from a ~/.dovecot.sieve.log (after getting a complaint that messages were not arriving properly anymore


I attempted this behavior on my setup to see what would happen. I changed the folder name and sent a mail which arrived in the main Inbox since there was no matching folder name. In the logs i saw...

   .active_sieve.log:
      fileinto action: failed to store into mailbox 'Catch_Testing': Mailbox doesn't exist: Catch_Testing.

   dovecot lmtp:
      sieve: Execution of script [redacted]/.active_sieve failed, but implicit keep was successful


Looks like "implicit keep" might be something to investigate.
According to https://doc.dovecot.org/configuration_manual/sieve/configuration/
it looks like implicit keep can be over ruled with discard or stop actions.