Internet Service Providers (ISPs) block ports such as port 25 to prevent spamming by their customers. This is the same with public places like café or libraries. Which will result to you not being able to send out emails any time. Vodien has an alternative port you can use, which is port 26. Learn more about editing mail servers or ports.
If the changes done doesn’t work, we recommend getting in touch with your ISP to check with them if they can enable port 25 or other ports you’ve used for you to send out email. Sometimes they’ll provide their own mail server for you to use so that you’ll be able to send out emails with no issues.
If you have other troubles other than ports, click the guided link for more idea about troubleshooting steps.