1.Start ADSI Edit. (Click Start, click Run, and then type adsiedit.msc.)

2.In ADSI Edit, from the Action menu, click Connect to.

3.In Connection Settings, under Connection Point, click Select a well known Naming Context, and then select Configuration from the corresponding list.

4.Under Computer, click Select or type a domain or server, and then in the corresponding box, select or type the name of your domain controller.

5.Click Advanced.

6.In Advanced, select Specify Credentials, and then type your user name and password in the corresponding boxes.

7.In the Port Number box, type 389.

8.Under Protocol, click LDAP.

9.Click OK to close the Advanced dialog box.

10.Click OK to close the Connection Settings dialog box.

11.In ADSI Edit, you are connected to the Configuration container of your domain controller.

12.Navigate to the following object: Configuration/Services/Microsoft Exchange//Administrative Groups//Servers//Information Store.

13.Right-click Information Store, and then click Properties.

14.On the Attribute Editor tab, click msExchESEParamCacheSizeMin, and then click Edit. Set to 8 (Do not set to zero or infostore will not restart)

15.On the Attribute Editor tab, click msExchESEParamCacheSizeMax, and then click Edit. set to (Do the Maths accroding to number of users.)

16.In Integer Attribute Editor, type the maximum size of the database cache, specified as the number of 8-kilobyte pages, and then click OK.

For example, to set the database cache size to 14 GB, divide 14 GB (14,680,064 KB) by 8 to get a value of 1,835,008 8-KB pages. In the Integer Attribute Editor dialog box, type this value without using commas or periods.

17.Click OK to close Information Store Properties.

18.Close ADSI Edit, and then restart the Microsoft Exchange Information Store service.

Some calculations for you on this one.

2gb = 2097152 kb = 262144
3gb = 3145728 kb = 393216
4gb = 4194304 kb = 524288
5gb = 5242880 kb = 655360
6gb = 6291456 kb = 786432

Exchange 2010 minimum required physical memory
No. of users =
1-10 = 2 GB
11-20 = 4 GB
21-30 = 6 GB
31-40 = 8 GB
41-50 = 10 GB
51-60 = 12 GB
61-70 = 14 GB
71-80 = 16 GB
81-90 = 18 GB