Chrome: Gmail Print All is a Chrome extension that lets you select multiple messages in Gmail and export them all to a Google Doc. From there, you can print, export to PDF or file away those messages with the rest of your important documents.
The extension works best when all of the messages you want to "print" are already assigned to a Gmail label, so make sure you do that first. Once you run the extension, you'll get a new Google Doc with all of the messages inside that you can add a cover page to, leave in Google Docs, or download and print in any format you choose. Each thread gets its own page with the subject line at the top, and the pages are all formatted for a Table of Contents, so you can easily add one and sort through the messages.
With tax season upon us, Gmail Print All is a perfect solution if you have a lot of order forms, invoices and other receipts filed away in Gmail but want to keep them with the rest of your tax documents. Similarly, if you just want to organise all of your account names, shipping notifications or personal messages to a loved one, Gmail Print All works like a charm.