Gmail Forward as Attachment provides the ability to download and/or attach to draft selected mail threads
Source code: https://gitlab.com/asfaltboy/gmail_forward_as_attachment
Inspired by multi-forward-for-gmail_, this extension aims to add the missing "download email" or "send email as attachment" functionality, commonly found in desktop email clients.
It does this by first finding the IDs of the selected threads in the mailbox, then fetching the RAW messages in given threads, saving them as in-memory File objects and finally providing download links for the files with ``<thread subject>.eml`` filenames. Additionally, an "Attach to new email" button opens a new compose window and attaches the files of the threads selected.
The UI interactions are provided by InboxSDK_, and the rest is done with Gmail-API_.