As far as performance , the size of the mailbox isn ' t nearly as impacting as the number of items in the 5 primary folders inbox , deleted , sent , calendar , contacts . With 2010 , there is a maximum supported # of items of 100 , 000 in these folders . Once approaching this max , or over , users will cause severely impacting performance hits to the mailbox server . I ' d check to see if anyone has maybe over 90 k items in any of the above folders , then deal with that , such as moving to subfolders . As far as the space , you could setup a retention policy to delete items over 7 years . Also verify the database isn ' t full of white space , as the database will never shrink until it is defragmented . 2010 does this automatically I think , but worth checking .