No emails are extracted from files containing lots of them

You have to check whether your files are plain text files. In fact, eMail Extractor was designed to process plain text files only. A plain text file is a file that contains human readable text. They are files you can open with TextEdit on the Mac and Notepad on the PC and read them directly. A binary file however is a file you can't read. It is made of binary code, something that looks gibberish to you. It will look as gibberish to eMail Extractor actually. An Excel file containing 3 e-mail addresses looks like this:

The same exact data saved as plain text by Excel and opened with a plain text file editor looks like this (here with TextEdit on a Mac, it is the same with Windows Notepad):

This is the reason why we say eMail Extractor can't process binary files. There are times however eMail Extractor will be able to extract addresses from given binary file. It is usually because the binary file contains a text block. eMail Extractor will process that block and will ignore the rest. It may work or it may not. We recommend you to never process binary files as you will most of the time get unexpected and random results.

There is a simple alternative to binary files, as most applications allow you to save your data as Plain Text. That includes Word and Excel for example. You just need to use the 'File -> Save As...' menu and select the plain text format. Once done your file will be fully processable by eMail Extractor.