Mailroom / incoming email IMAP folder keeps filling up, should be cleaned automatically

Summary

Mailroom / incoming email IMAP folder keeps filling up, should be cleaned automatically

GitLab 11.0 using Exchange backed IMAP for mailroom

Steps to reproduce

1. Setup reply by email
2. Send lots of reply by email until mailbox fills up
3. Get rejection that mailbox is full

What is the current bug behavior?

Processed emails still saved in mailroom / incoming email IMAP folder

What is the expected correct behavior?

Processed emails should be deleted from mailroom / incoming email IMAP folder

Related

Reopening of https://gitlab.com/gitlab-org/gitlab-ce/issues/33498