Are you tired of allowing umlimited mailboxes to Execs that want need 3GB mailboxes?  Now you can set warning, no send and no recieve limits that are higher than the 2,097,151 KB.

The whole article is here.

The gist of it using ADSIEdit or your favorite tool to manually modify the mDBStorageQuota, mDBOverQuotaLimit  and mDBOverHardQuotaLimit properties.

For a specific user

1. Open the domain context of your domain in ADSI Edit
2. Open the properties of the user.
3. Show optional attributes.
4. Open mDBOverHardQuotaLimit or mDBOverQuotaLimit  or mDBOverHardQuotaLimit.
5. Edit the value in kilobytes that you want to set, and then click OK. (For example, to set a limit of 3 GB, type 3145728)

Setting this for a mailbox store is similar however in ADSI edit you locate the server in configuration context

Configuration [Domain]\DC=Configuration,[Domain],DC=[Domain Root]\CN=Services\CN=Microsoft Exchange\CN=[Org Name]\CN=Administrative Groups\CN=First Administrative Group\CN=Servers\CN=[Exchange Server]\CN=Information Store\

Then you would select the mailbox store and make the same attribute changes as you did above for a specific user. 

Note:  Making these changes will keep you from making any changes to these databases or users in ESM.  You will need to make future limit modifications following this same procedure.