Before you start setting up your email client, please be sure to create an email account in cPanel.
In your cPanel go to
Mail > Email accounts
The email account should be in the list of existing email accounts, otherwise you need to create it.
SMTP: 25 or 26
Sometimes internet service providers filter port 25 in their network for internal reasons. If you fail to connect to SMTP via port 25, try port 26. If using port 26 results in failure as well, please try using port 465 with SSL protection enabled.