You really need to talk to your VPS provider and ask them about firewalls.
Is firewall installed by default and if so, is it set to block by default and you have to open ports, or is it set open (or not installed), in which case you'd have to block ports.

Don't ask me about firewall SW; it's been years since I messed with it, and it was a completely different distro.


Note that just because a port is not blocked, as long as no server SW is listening on that port, it won't be used.
In other words, in practical terms, it's not an issue - in strict security terms you should block any ports from incoming calls, unless you are using them.
Cmd to chk for ports being used ( run this cmd as root)
Do NOT try to change the default port nums that server SW eg SSH, SMTP etc use.
Also, FYI, any port num < 1024 can only be used by root owned processes. This is not a problem, as any SW that needs that will also need to be installed by root user anyway.

HTH

PS Ask them about those 'missing' cmds as well.

To: chrism01
I have open port: 22 Secure Shell (SSH). I have closed port: 25 Simple Mail Transfer Protocol (SMTP). I am trying to open port 25. Thank you for trying, but your last post was not much help. It sounds like you did all you could. I did talk to my VPS provider and ask them about firewalls: And I told you the reply. I agree the reply was vague. As one port is open and the rest are closed, I guess that a firewall is installed and running. Or what else can cause this? I already checked for ports being used: I know that answer. As you recommend, I will not try to change the port numbers, I am simply trying to open one more port. I will not ask my host about missing commands: If I want a command, I will simply install the package. I delay package install until needed because I like to keep my system install fresh.

This thread is very confusing. Why do you think port 25 is closed? If it is closed, why would you open port 25 if you have not setup a mailserver listening? A mailserver needs more ports then just port 25. You might want to do some reading first. If you do not set it up in the right way, your server will be a spambox, or worse. Read about security before starting.
Upgrading to debian 11: example.

From what I read in your posts, I would strongly advise you to have a look at "mailcow - dockerized", as said before. it is an all in one solution, setup in docker container. (using: postfix, dovecot, nginx, rspamd, mariadb, redis, etc.)

To: giesbert
The thread is very confusing because I do not know much about this subject. And I started with little. Later, I did get a better VPS. You may ask questions to clarify.

I think port 25 is closed because https://www.whatismyip.com/port-scanner/ (and many other sites) say it is.

iredmail Instructions say: before installing software, open port 25.

I do not know what a mailserver list is, I guess iredmail software will make one or tell me how to get one when it is time.

I am preparing my VPS for installation of iredmail. And doc says I need open port 25.

I have done much reading. My priority is to get it running. Later I will worry about spambox.

I did follow your advice and looked into Mailcow. Thank you, that was very helpful and I chose a similar product: iredmail.

This is taking me a long time because I got sidetracked and I am reading. I wish to satisfy prerequisites before installing software.

I got iredmail working. The port automatically opened when I installed. I wish I knew why. This seems to counterdict the documentation. I now mark this thread as solved.