Mail fetch accounts filter into the INBOX
 

At least they do when I posted this...

FastMail, not knowing when to leave stuff stuff that works alone, decided to change the way they handle mail fetch account's "Deliver to" folder. Apparently doing Sieve fileinto's is not "good enough" for them so they changed them to using the "new" (JMap?) implicit_keep_target. That's apparently doesn't work and all your mail fetch accounts will deliver email sent to them into your INBOX!

This implicit_keep_target is also how they implement the "My email addresses" new "Move to a folder" rule operation so that probably doesn't work too - didn't test it except to see what the Sieve code was for it for one of my addresses. Makes me wonder if they ever tested it too!

I assume the implicit_keep_target call that specifies the target destination is handled by the processimip call further down in the Sieve code (the function's name choice seems about right). That call has chocked Sieve Tester since the day it was put in (long before the implicit_keep_target's)! If you are using Sieve Tester with your full Sieve script remember to comment that line out. Maybe if it's choking Sieve Tester it's possible it's also choking the actual Sieve interpreter as well and that's why stuff ends up in the INBOX. Nothing ever used implicit_keep_target before so the pre-existing processimip had nothing to do so it probably exited ok - not in Sieve Tester though. Not sure about the details, just guessing here.

At any rate, this is just a heads up. I just submitted a ticket on this.

I was notified a couple of days ago that they fixed the mail fetch problem and apparently they have! :)