I have “Mailing list mode” enabled in my preferences, and also “Include previous replies at the bottom of emails”.
In the pure-text (non-HTML) version of such e-mails, the replies for a thread (e.g. Ideas for a Rayon logo) have links to images of the form
upload://... which means it’s not possible to view them.
In the HTML version (as well as in the web UI) they have the form
https://discourse-cdn-sjc1.com/business5/uploads/... It would be nice to have these full URLs in the text version too.