Verify e-mail formatting

[sinus-x]

Now, the images are being loaded from Discord CDN. It's not ideal, because they aren't displayed unless the user clicks some button, which I doubt most of them do, even though we have no data about this.

We may try including the images as attachments and linking to them in the code, but @czechbol did that a year ago and it still required the user to click the button to show them, if I recall correctly.

Perhaps we should abandon that idea and only include their usernames.