I can’t seem to send Mails to gmail addresses or anywhere.
Under queue it shows that it can’t connect to the gmail host on port 25.
It’s probably my ISP that is blockign Port 25.
How can I change the Port?
Changing that port won’t solve your problem since every mail server connects via this port. You have to ask your ISP to open the port or choose another ISP.
Are you sure about that? I’ve read that Port 587 and 465 would be secure and are the solution for this.
Yes, but no. E-Mail-Clients use those ports for encrypted communication. The relaying between servers happens exclusively on port 25 afaik. If your server supports TLS it will use the encryption on 25 anyways. I think there is no workaround for using port 25.
That’s what I told my ISP, that encryption is possible over Port 25 too but they declined. Oh well, too bad.
https://serverfault.com/questions/1033089/can-i-configure-postfix-to-send-outgoing-emails-to-port-other-than-25/1033093 You could send one of the endless explanations to your ISP. Or choose a competent one. In the Mailcow Telegram Group this one https://www.eth-services.de/ is recommended often, because it has a clean IP-Range for sending mail alternatively https://contabo.com/de/vps/ offers very cheap servers which work too but the IP-Range isn’t clean since some use it to send spam. If you are on a residential connection and cannot change your provider, you could install a relay on a VPS somewhere and tunnel traffic though a VPN or directly.