My experience (we run the same EX5.5 Version) is that the .edb file a dynamic ‘file’. So i grows until 16GB and then it stops working (we had this last year). When the system says it’s 4GB it is 4 Gb large. When it’s says it’s got x Mb free, it just indicates that there’s place (x Mb) free before the 4 GB starts to grown. I’m pretty sure you’ve got 12 Gb free space (16-4). Oh yes, 16 Gb is the limit for Exchange 5.5 !!