solving the smtp settings of Internet operator

In Finland it is possible to use port 25 for sending an email only the smtp-server of the internet interface operator.

Most often used operators in Finland and their smtp servers' names:

-Elisa: smtp.kolumbus.fi

-Dna-internet interface: smtp.dnainternet.net

-Dna-mobiili interface: smtp.dna044.com

-Telia: smtp.tele.fi (old Telia: mail.inet.fi )

If you don't know the operator of the used internet interface, you can check it from e.g https://www.whatismyip.com/ip-whois-lookup/  by giving an existing network's public ip address to the IP field and pressing 'Lookup'

The public IP address can be checked from a controller's menu > settings > ip-addresses, where in the bottom of the page there is a mention of the current time (if an internet connection exists) and the IP address of this device at that time.
example:

updated 11.8.2023:
-Telia: smtp.tele.fi (old Telia: mail.inet.fi )