Normally, a Quota exceeded error is returned if saving/copying a message would bring the user over quota. With the trash plug-in, instead the oldest messages are expunged from the specified mailboxes until the message can be saved (the error is returned only if all messages in those mailboxes together take up more space than the message being handled).
This parameter points to a text file that configures the plug-in’s behavior.
trash = /etc/dovecot/dovecot-trash.conf.External
The file uses the following format:
<priority> <mailbox name>
Deletion begins with the mailbox that has the lowest priority number and proceeds from there.