Google Activation Guide Postini Email Security - Manual (Page 46)

52 Activation Guide
What happens if I type the wrong information into the MX record?
If you type the incorrect delivery information in the MX record, some mail will
bounce. The sender will receive a notice that the mail wasn't delivered. If this
happens, correct the MX records as soon as possible. Some mail may still bounce
for a period of time (up to the length of the new TTL setting), but the sooner you
update the MX records to the correct setting, the fewer messages will bounce.
What happens when I update my MX records?
Once you update your MX records, mail will start flowing through the message
security service. After your old previous TTL (in seconds) has expired, all your
mail flows through the message security service. When your mail flows through
the service, mail is bounced from IP addresses known to be a major source of
spam attacks or viruses. Also, if you have Non-Account Virus Blocking, mail to
users will be filtered for viruses as well. You'll get complete mail filtering after
you've added your users.
How can I tell if the MX update worked?
Send a test message from an outside address, then view the full headers. The full
headers are about 20-50 lines of text. If the headers include the word "psmtp.com"
then the mail flowed through the message security service.