Optimizing leads from email inbox

[Matt Zale]

I imagine everybody has an email inbox full of leads or other good info to be organized. Generally, how does the BP community make the most out of their email inboxes? Any helpful extensions or software? I use Mac with Gmail & Google Drive mostly.

Background on my specific task -- need to organize email content from various Google or Yahoo investor groups (Yahoo forwards to Gmail). Over the years they've compiled to appx 50,000 emails and I'd like to convert this to a Google Sheet with a few columns (title of message, body of message, email address of poster, date posted, and if possible files & photo attachments). Mostly want to reach out to private lenders, cash buyers, rehabbers and other deal facilitators. 

I've tried 'Google Takeout' which resulted in a .mbox file that I can't open. Not even sure what it'll look like if I do open it. Then I downloaded Mozilla Thunderbird but with a 'server not found' error. Seems like a great program but a bit much for my needs.

Just need a bunch of Gmails to move to Google sheets. Any thoughts, suggestions, solutions?