Google Message Security for Google Apps Administration Guide - Manual (Page 51)

Organization Management 51
Handle Mail to Unrecognized Addresses
Once you add a domain to the message security service, all email to that domain
is routed through the data center. Only addresses recognized by the data center—
that have been added as users, for example—receive filtering. But email to other
addresses in the domain—to users that aren’t yet added to the service, that aren’t
receiving protection, or that don’t exist—must be dealt with, too.
Note: An address is recognized if it’s been added to the service as a user or user
alias; if it’s supported by a domain alias. See “Manage User Aliases/Nicknames”
on page 78, “Add a Domain for Filtering” on page 236.
When users are passed through without filtering
If you turn off Non-Account Bouncing for an org, thus passing messages through
to unrecognized users, without filtering them, those users still receive certain
protections:
Unrecognized Mail Option Org General Settings
Bounce the message • Non-Account Bouncing = On
Messages to unrecognized users are
bounced, never reaching the intended
recipient. The SMTP error:
550 No such user
- psmtp is returned to the sender.
If your Google Apps account has catchall
enabled, Non-Account Bouncing must be Off.
WARNING: You must configure these settings
for an org that contains your domains.
Deliver the message, without
filtering or adding it to the
service • Non-Account Bouncing = Off
Messages to unrecognized users are
delivered without filtering. No users are added
to the message security service.
Use Case: Use this option to allow everyone
in a domain to receive email, even if they
aren’t all added to the message security
service.
WARNING: You must configure these settings
for an org that contains your domains.