I don't think quota full should be logged as an error.. Without Sieve this is logged:
Info: msgid=unspecified: subject=: save failed to INBOX: Quota exceeded (mailbox for user is full) Info: msgid=unspecified: subject=: rejected: Quota exceeded (mailbox for user is full)
Also when this happens, does quota_full_tempfail setting work as expected?
I haven't tried the quota_full_tempfail yet, because a lot of these are just accounts that haven't been used forever and have gotten full of spam and I dont know if I'd prefer tempfailing them to just bouncing.
Most of these accounts in question just have a simple .dovecot.sieve script generated by roundcube that only has "/* empty script */" in it. I assume that's why sieve is responding at all with a "failed with unsuccessful implicit keep".
Any chance sieve can just not worry about processing anything if there's nothing but comments in the .dovecot.sieve file? :)
-c