Floating IP Firewall/Iptables configuration

Hi there,

I’m working in a assignment, beginner in networking and need your help regarding Iptables/FIREWALL.

My droplet has a floating IP x2.x2.x2.x2 , and same droplet is sending emails by itself using my public IP x1.x1.x1.x1 .

I don’t want to show my droplets public IP in mail header neither in SPF, as it is one of the requirements.

[Method one] Use Floating IP for SMTP

I tried this solution . I’m not able to achieve the same, and as I can understand DigitalOcean is blocking outbound connection using floating IP for SMTP.

I was not successful applying this,

[Method two] Block all traffic outbound/inbound in Public IP x1.x1.x1.x1 except SMTP, and Allow normal traffic into Floating IP 80, 22, 443, etc

So even it shows the IP of the droplet but it will only work for email service.

Applying this, is a bit confusing since what I believe Digital ocean cloud firewall is not capable of controlling the Floating IP and I’m not that good in networking.

Can any one please help me, how can I achieve that ? do you have another suggestion ?



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Personally I would recommend against running your own mail services whenever possible. There are free and low cost hosted options available which remove the burden of administering these services.

Should you choose to set up method 2 above you will want to configure a firewall on the server itself rather than on your floating IP since you’ll be sending directly. This guide includes details on setting up FirewallD on CentOS. You can use this to set up a local firewall and open SMTP ports.