The software Email Address Extract (via Ades Blog) works surprisingly well. All you need to do is point it at a folder on your hard drive and select the file type that should be crawled. Some preconfigured files types are htm, log and dat but it is possible to use wildcards or other file types as well. The option to process subfolders automatically could be worth checking as well.

The scan itself does not take longer than a few seconds normally. I did test it on one of my mailbox files in Thunderbird and it did extract more than 6000 emails from that which means it works practically with all files that contain text. Doubt it will be highly successful crawling binary files.

Emails that have been found can be exported into a text document for further processing. They can be sorted by username or mails server before doing so.