Google Outbound Services Configuration Guide - Manual (Page 39)

Microsoft Exchange 2007/2010 (Private DNS Method) 41
5. Select “use these DNS servers:” and enter the appropriate IP address for your
system. Press enter to add the address.
The appropriate IP address depends on your system. To find what system to
use, see “Identify Your System” on page 13.
System IP Address to use for Private Outbound DNS
5 64.18.4.12
6 64.18.5.12
7 64.18.6.12
8 64.18.7.12
9 74.125.148.12
10 74.125.244.12
20 64.18.9.14