[Dovecot] trash plugin

[Cor Bosman]

The trash plugin docs say:

"Normally if a message can't be saved/copied because it would bring user over quota, the save/copy fails with "Quota exceeded" error. The trash plugin can be used to avoid such situations by making Dovecot automatically expunge oldest messages from configured mailboxes until the message can be saved"

This leads me to believe that if a message cant be stored, the plugin would avoid returning a quota error, but instead delete/expunge messages until the original message can fit, and then complete the command. 

But I see something different, at least using the plugin in imap (havent tried it on lmtp). When I drag a message to a folder thats almost full, and the message doesnt fit, I get an actual quota error:

23 uid copy 454343 "Spam"
23 NO [OVERQUOTA] Quota exceeded (mailbox for user is full)

After my client sees this error, I see the trash plugin creating space. But then it's too late right? The client already has a visible error. Am I just misunderstanding how the trash plugin is supposed to work? 

Dovecot 2.1.4, config is on a set of test servers:

namespace {
  type = private
  separator = /
  inbox = yes  
}

namespace {
  type = private
  separator = /
  inbox = no
  prefix = Spam/
  location = maildir:/var/spool/mail/%1u/%1.1u/%u/.Spam:INDEX=/var/spool/mail/dovecot-control/indexes/%1u/%2u/%u/.Spam:CONTROL=/var/spool/mail/dovecot-control/%1u/%2u/%u/.Spam
  subscriptions = no
  list = yes
  hidden = yes
}

plugin {
  quota = maildir:Spam quota:ns=Spam/
  quota_rule = *:storage=5000K
}

My goal is to create a FIFO spam folder that never returns a quota error, but instead just deletes the oldest emails as new spam comes in.

Regards,

Cor