Hi Vipul,
the background why we want to delete the messages is that we had a spam attack with lots of spam profiles coming into Campaign via a landing page form.
Reasons for failing to send the transactional message were mainly that the email addresses did not exist, users did not exist or emails bounced. Please find in the following a screenshot of the sending logs of the transactional message:

Exlucsion causes were for all messages: "Quarantined address (Quarantine)"
So what I did was to select the erroneous messages in the message center execution overview and clicked "delete element", as shown in the next screenshot:

We unpublished the transactional message meanwhile.
Was that proceeded ok from your side or should I ask for some database cleanup?
Thanks again,
Lena