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SMTP servers behind Firewall

This is one of the simplest configurations to implement.Install our SPAM Filtering software on a standalone server.Reconfigure the firewall so that it routes the external IP address to the IP assigned to SPAM Filter.The SPAM Filter server will now be receiving all internet email and will then forward legitimate emails to your SMTP server.

Multiple SMTP servers behind firewall DNS MX record: mail.domain.com · Firewall NATs the external address to your mail server. After: DNS MX record remains mail.domain.com · Firewall now routes incoming mail to SpamFilter. SpamFilter: 10.10.10.3 → Your mail server: 10.10.10.2 Email clients continue using 10.10.10.2 for outgoing SMTP. BEFORE DNS MX record: mail.domain.com · Firewall NATs the external address to your mail server AFTER · WITH SPAMFILTER DNS MX record remains mail.domain.com · Firewall now routes incoming mail to SpamFilter Internet Incoming SMTP Firewall External SMTP port 25 Your mail server 10.10.10.2 port 25 Email clients SMTP: 10.10.10.2 port 25 SMTP Internet SMTP: port 25 Firewall NAT → 10.10.10.3 SpamFilter 10.10.10.3 Mail server 10.10.10.2 Email clients SMTP: 10.10.10.2 SpamFilter: 10.10.10.3 → Your mail server: 10.10.10.2 Email clients continue using 10.10.10.2 for outgoing SMTP. Incoming mail → SpamFilter → Your SMTP server