Helfertool can parse incoming mails and extract the non-delivery reports. Therefore, an IMAP mailbox is required that contains these incoming mails.
The tool only marks the handled mails as read, but does not delete them.
If you also want to delete old mails, you can use the mail-cleaner.py script to achieve this.
It uses the same helfertool.yaml config file as Helfertool:
./mail-cleaner.py [--dry-run] --config /etc/helfertool/helfertool.yaml --days 90
This would delete all mails older than 90 days in the configured mailbox and folder.