How do you backup your email extender server?

It seems to be a headache for us. We have Lotus notes. We just installed email extender and the container volume is already 2.5Tb in size and it is expected to grow even larger. It takes 45 hours or sometimes longer to do full backups of all that data. The must be a better/faster way to do it. We are using netbackup and have a separate stream for that volume. Could you share your experiences with backups of that container volume.