Changing your server settings is a little bit hidden so we have created a little guide for this.
To get to the right settings, first click on "File" or "File" if you have the English version.

Then select the account whose settings you want to change (1) and click the small arrow at the bottom of the button (2).

Then click on server settings.

You will now see the options for the incoming server.

You can also view them for the outgoing server.

Bear in mind that you may have different settings for different providers. If something is not working, send screenshots of the above settings together with your error message to your provider so that they can help you solve the problem. In almost all cases, it is a minor adjustment to your settings that causes it not to work. This is because the requirements for secure emailing are getting tighter.