Google Outbound Services Configuration Guide - Manual (Page 13)

14 Outbound Services Configuration Guide
Note: Both sets of IP ranges are applicable for system 20 customers.
Set Up Reinjection
Reinjection is the process of queueing a message back to the customer’s server
when it cannot be delivered due to conflicting SMTP errors after DATA. The
reinjection host is often the same server as the outbound server, but this is not
required.
Reinjection is necessary to avoid unexpected mail loss for a messages sent to
multiple recipients. Fewer than 0.1% of all messages are reinjected. Before you
can route mail through Outbound Services, the Administration Console checks
that your reinjection host is configured to allow the email security service IP
addresses to relay for external recipients.
You may have already set up your mail server and firewall to accept messages
from the email security service, but reinjection requires further access. Your
reinjection server must accept mail from the email security service and send it out
again. This is called a private relay.
Configure your mail server and firewall to accept email only from the email
security service. Your reinjection host needs to accept all email from the email
security service’s outbound servers. From your server’s perspective, the email
security service’s delivery servers should be considered a trusted server. Allow
relaying only from the email security service’s IP range and other trusted relay
servers.
If you have multiple mail servers, specify which server (or servers) will act as the
reinjection host, and be sure that server can route mail back to the email security
service.
Be careful when you set up a private relay. If you allow all IP addresses to pass
mail through your server, your mail server will become an open relay. This leaves
your mail server vulnerable to hijacking from malicious senders. Setting up a
private relay is safer than an open relay, since malicious outsiders cannot use a
private relay in the same way.
Setting up reinjection is different for every mail server type. For step-by-step
instructions for setting up reinjection, see the appropriate chapter in this guide for
your mail server.
System IP Range CIDR Range IP/Subnet Mask Pair
5, 6, 7, 8, 20 64.18.0.0 -
64.18.15.255 64.18.0.0/20 64.18.0.0
mask 255.255.240.0
9 74.125.148.0 -
74.125.151.255 74.125.148.0/22 74.125.148.0
mask 255.255.252.0
10 74.125.244.0 -
74.125.247.255 74.125.244.0/22 74.125.244.0
mask 255.255.252.0
20, 200,
201 207.126.144.0 -
207.126.159.255 207.126.144.0/20 207.126.144.0
mask 255.255.240.0