In order to process e-mail messages stored into the Apple Mail application you have to save those messages to a plain text file first. Just go through the following steps:
1.- Select the messages you want to extract e-mail addresses of.
2.- Select the File > Save As menu.
3.- Set the format to Raw Message Source and do not include attachments.
4.- Click on the Save button to create the output file.
Lauch eMail Extractor and drag and drop the file to it.
6.- The file is processed and e-mail addresses extracted.
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