strnisa

Yes, you can remove attachments with Thunderbird, but it requires a lot of configuration and it is highly error-prone. Disclaimer: I'm the author of Unattach.

It is a client-side app that runs inside the browser. Or do you mean something else?

Does it work for all types of attachments (e.g. inline) and can be done across many emails at once? Can it add information about what was removed?

Yes, Gmail API does not support this out of the box. However, you can download the raw email, update it locally, upload the modified copy, and then delete the original. This is how the web app (Unattach) described in the blog post does it. Disclaimer: I am the author.

I believe that it would be possible to make it into a website, yes.

The main reason why I haven't gone this way is because of the trust issue, which most users care about. At the moment, user data flows only between the Google servers and the user's local computer, which is easy to check. With the website, it's harder for the user to know that the Unattach server doesn't store private data.

In addition, it's more complicated for a web application to store data to the local filesystem.

The main benefit of using Unattach over simply deleting the emails is that you can keep all the other parts of your emails in your Gmail server. These are often valuable, don't take much space and can continue to be searched. Unattach also provides various facilities to make finding and storing attachments in custom directory structures easy.

If you'd like to free some of that 15GB, you can bulk remove some attachments from your Gmail with Unattach. It's free and open-source: http://unattach.app/

Full disclosure: I'm the author of Unattach.