I needed a way to quickly get all email addresses out of a Google Apps account. I found a solution by Helge Klein, Extracting all Email Addresses from a GMail Label.
His Google Sheet has a Google Apps Script that:
The script extracts email addresses from all messages in all threads tagged with a given label. It processes even large numbers of emails quickly. In addition to the sender’s email address it lists the sender’s name and the date of first communication.
Visit his article to see a proper guide on how to use it. But essentially, all you have to do is copy to your Google Drive for the Google Account you want the emails from, enter the label (or leave blank for all labels) and press HK Scripts > Extract all email addresses. Give it some time and the addresses will appear in a tab called “Label: label-name“.
Incase the Google Sheet shared by Helge Klein disappears in the future, I have made a copy you can reference on my Google Account. Copy the Gmail email address extract template.