I check on a weekly basis the size of the information store. It has increased in size for weeks by around 500mb, I checked this week and it has stayed the same size as the previous week. It also has a modification date from last week. How can this be? The server has been up and mail has been moving. Thanks for any help...

The modification date not changing isn't a problem. That only changes when the file system updates it, and that only occurs when the service is restarted. Looking at my own server the last modified date is 20th December 2010. As for the physical size, again not unusual. Exchange looks after itself and will use "white space" in the database before increasing in size. This white space is where content was located in the database which has been deleted. Look for event ID 1221 in the event viewer overnight to see how much white space there is in the store. Therefore nothing you have said is an indication of a problem with the server. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources

Thanks never noticed that before.