There are many options for cleaning up emails on the server. Once you remove these emails they will automatically be removed from your outlook application as well.

1. Log into your control panel. Click here to login.

2.  Click on Email Account

3.  Click on Manage

4.  Click on free up email storage

5.  Enter the customer query eg: SUBJECT "Mail delivery failed: returning message to sender"  to delete all email that has the subject Mail.....

Here are a few more options you can use for the custom query as well:

SEEN
Matches messages with the IMAP flag \Seen set.

UNSEEN
Matches messages, which do not have the IMAP flag \Seen set

SUBJECT string
Matches messages, which contain string in the SUBJECT field of the message's IMAP envelope structure.

TEXT string
Matches messages, which contain string in the message headers or body.