The important thing to remember is although these email programs accept a variety of formats (xls, .xlsx, .csv, .txt for example), you will need to have a clean file for upload.
If there is special formatting in your file that isn’t compatible with the email program, you may need to save it in a different format.
For example, if you have multiple email addresses for one contact, you will need to clean up your file and separate the addresses. In the screen shot below, you can see there are three email addresses for one contact. Each email address would need it’s own row in a spreadsheet.
Each email program will have specific methods to import the email lists.