To delete all the admin messages (tickets) from direct admin control panel:

1. Goto this folder /usr/local/directadmin/data/tickets
   # cd /usr/local/directadmin/data/tickets

2. Delete all the folder content, which is the messages
   # rm -Rf *
3. Clear up the messages database file
   # echo "" > /usr/local/directadmin/data/admin/tickets.list

All messages should be cleared now, mostly those messages are from the brute-force attack logs, if you don’t mind about such messages you can disabled this feature in DirectAdmin control panel.

To achieve that, from the DirectAdmin Panel -> Extra Features, click on Administrator Settings and choose No for the Security Option Parse service logs for brute force attacks