Delete clientmqueue mails

My clientmqueue directory is almost 6.7GB. There are like a thousands of e-mail that are present. Is there any way to delete them or just delete them normally. Also while deleting them, do i need to shutdown my sendmail service?

Root FS is almost at 100%. Please help in this.

Thanks in advance.

To get quick results with less prone
1- Stop the sendmail daemon ,
2- rm /var/spool/mqueue/*
3- Start sendmail again