You don't need a static IP.
It all sounds like the port forward didn't work. Try a port check tool and let it check if it's really open. You will need a desktop tool not just some website.
I used this once https://portforward.com/help/portcheck.htm. Set it to UDP and check.

arma 3 runnig server

Program claims that all of my ports are blocked when arma not running. Even http (80-88) and stmp (25).

This webpage claims otherwise http://www.ipfingerprints.com/portscan.php

test of program (same that claimed that ports were blocked) while arma was running server:

These tools say ports are blocked when there is nothing listening on it.. Which makes sense for http smtp and others.
And my tool wasn't working because it needs to access the port itself. So it can't work if Arma already blocks the port.

I probably know what is the true issue: progress. Progress of the internet infrastructure.

I'm just behind NAT. What internet provider want's to sell me is not static IP, but outside IP.

There is term "NAT punch", but I don't know how to do it.

Dev should look into this in the future, because I countered some voices on internet saying that more and more ppl with fast-new-shiny internet are behind that kind of wall.

@MadogPL Mostly this happen when you have a IPv6 active. The provider uses a IPv6 on your connection (to not use valueable IPv4) and routes your traffic to a Server with a IPv4. As that server handles many Users a port forwarding is not possible. BUT as you pay your provider to have internet and he does not (mostly) limit the usage to specific applications you can call your provider and as an example say your NAS is not working and that they pls should provide you with a IPv4 (mostly its then even static). Thats a easy way to fix that problem and even works on approx 80% of providers

I can buy "outside" IP. But this is extra money. And it's like 1/3 price of the internet cost. Just to host Arma.

I only hope, that dev will think about future, to bypass NAT.

I dont mean a static IP Adress i really mean just a generic non static IPv4 adress. Just tell your provider that you cannot use your internet and if they do not comply that you will need to change the provider that mostly works

That might have worked months ago. They know I've got good internet.

And I did not ment static IP. It's outside IP. It's different. Literally I pay to have an ability to forward ports.

It's a dev issue for me :( No other game has this issue. On other hand, I don't host servers of other games. But, if I want to play with someone I did not have problems with that. Either they have servers to host games, they somehow avoided NAT or something else. For me, it's Arma3 issue.

@MadogPL Tha's wrong. Game like Ghost Recon Wildlands had open NAT, and now strict NAT, on some providers, whatever the port you open.
The only solution I found is to make a DMZ which is strongly not recommended.

The NAT, NAT2, NAT3 now is a total mess, not depending only on BI.