Cant figure out if my ISP blocks port 25 or my configuration is wrong!

Hello, I am very new in this server world. After a month of research, I decided to go with HestiaCP.

I got an old celeron pc and I made it my “testing” server. Basically I want to learn all about servers using it.

Now I am stuck at sending emails. My ISP originally blocked port 25, but they unlocked it at my request.

I am not able to send/recive emails from email addreses hosted on other place then my server. Between my server emails the send/recive proces is instant.
But things get even more weird!

I am able to setup my email on my phone using my cellular data, and I can send/recive emails between all the emails hosted on my server, but still cant send to an gmail, yahoo, etc.

I tried to send from gmail to one of emails hosted on my server, and google send me this email error back, after half a day:

When I telenat gmail smtp server

i get this message after a long time waiting :

telenat gmail smtp server 25
Trying smtpserverip…
telnet: Unable to connect to remote host: Network is unreachable

When I do a DNS Propagation Check on, they point to my server’s public ip addres, all good.

But if i do

telenat gmail smtp server

I get :

telenat smtp gmail server 465
Trying gmail smtp gmail server…
Connected to smtp gmail server

The thing is that I can’t send NOR recive emails from other server then mine. I can’t find someone having this problem on the whole forum. They either cant recive or send mails AT ALL, but I can do it from every network( my 4G connection, my friend’s house etc) ONLY if i send it to another email hosted on my server.

Is a bit frustrating, because I am new and I can’t really tell what I’m doing wrong, because it works in proportion of 80% i’d say.

Anything else is working great on this panel, and i Really appreciate your effort guys, I really like this domain and I hope one day I could be part of something like this, but now I’M stuck, and every thing I do from similar topics won’t work.

All the tutorials are with paid virtual servers that have ubuntu installed and all the hard part already done (for me at least). Like setting up ubuntu as a DNS & HOST server (because i cant aford another 2 pc-s for making a DNS cluster).

And no,I don’t think the solution is to use other DNS servers, or get a paid service, because my goal here is to learn and maybe host some Wordpress sites for my friends.

So i think my ISP is still blocking my port 25, even if they told me it is unlocked now.

Here are other setting that might help you understand my problem.

PORT FORWARDING/VIRTUAL SERVERS with the internal ip of my ubuntu 18.04 server:
I port forwarded this ports from public ip to my ubuntu server machine internal ip: 995, 110, 993, 465, 25, 587, 143, 53, 80, 8000, 8080,22,21.
I also added this ip to DMZ and activated it.

When i do a telnet to my

telnet mail dot my domain dot tld 25
Trying mail dot my domain dot tld server…
Connected to mail dot my domain dot tld
Escape character is ‘^]’.
220 hostname dot tld

Altough it seems a bit weird how instead of getting a “220” I get it with the domain of the hostname dot tld instead.

I also can login to every email with roundcube from everywhere, but can only send emails internal, that can be viewed from everywhere.

Sorry i wrote telnet results like this, I am a new user and i can use more then 2 links in one topic, and it looks like ip address, even if i write it wrong counts.

Coming up with news, the port 25 is still blocked, altough on my ISP service panel is telling that they unlocked it.