All Email Security Gateways, all firmware versions.
There are a few different reasons spammers will send email directly to your mail server, even after you install your Email Security Gateway.
- Spammers send to every MX record for your domain. This means that if you have your mail server listed as a lower-priority MX record (as a failover), spammers will send directly to the failover MX host as well. If you need redundancy, the best method is to use two Email Security Gateways in a cluster (available for models 400 and above).
- DNS Caching. If your mail server has been removed from your MX records, some spamming servers may still have its address cached as a valid SMTP recipient. This means they may continue to send directly to your mail server.
- "Spam bots" may be port scanning random IP addresses, and if your mail server is open and accepting SMTP connections from the internet, they may begin spamming you.
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