Configuring POP and SMTP settings can be tricky sometimes.
Whatever email provider you're using also has a HELP section on how to configure most common email applications such as Outlook and Thunderbird. These instructions are usually very concise and easy to follow, just take your time.
If you're still having trouble then it is best to get help from your ISP tech support.
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Personally, I prefer to access my email from my browser since it much safer that way and less issues with spam, sometimes malware, trojans and such can sneek in when one uses an email application.
Just my 2 cents on that!