Incoming SMTP mail and iptables firewall

It would depend on how you've setup postfix. What are you doing with postfix exactly? It is a "send only" system, or do you actually want to be able to receive emails?

If its a send only system, then there is no reason why you should open port 25 to the public, better to keep it closed.

In my case, I use CentOS 7, which uses firewalld/systemd, so I am not sure about the iptables command.

@patrick_here:

I have setup postfix on my linode.

Do I need to open port 25 for incoming with something liike:

iptables -A INPUT -p tcp –dport 25 -j ACCEPT

…and if I do are there any risks other than the possibility of receiving some spam?
It could be even worse: You could receive real email (non-spam) that you have to handle. :D

Do you really want to receive email at the yourusername@yourmachine address?

Enabling postfix and allowing port 25 automatically makes such address to be reachable.

It won't make any emails reachable automatically, unless he has setup postfix properly.