IP Address ranges for SMTP services
Posted by Helpdesk Admin on 27 July 2009 10:13 AM
If you operate a firewall that blocks inbound SMTP email on port 25, you will need to open access on this port to the following IP addresses in order to ensure proper mail delivery to your in-house mail server. In the case of Spam Filtering services, you need only allow the relevant ranges and block all others to prevent emails bypassing the filtering servers.
MX Backup and SpamFilter.ie
Postini (Discontinued from June 2013)
Symantec.cloud (replacing Postini from June 2013)
If you run your own connection time spam filtering on your email server, we recommend that you additionally whitelist all the above ranges in your system, in order to prevent false positives or other relaying issues.
This is especially important for MX backup as otherwise automatic relaying of messages after an outage may not happen reliably.