Because DMI stores the email message in DayLite, databases can become very large. That's not a problem. however you will want to take a few precautions:

•     Ensure you have enough room on the computer that is running the DayLite databases
•     Strip attachments before sending the emails to DayLite (there is option for this in the DMI drawer)
•     Make sure your computer is using 'network time', especially if you have offline databases
•     Setup a nightly backup process (remember to account for the database size!)