www.fastmailusercontent.com is blocked, but it's point is to avoid tracking by loading images using a proxy.

[Wizardling]

www.fastmailusercontent.com is blocked, but it's point is to avoid tracking by loading images using a proxy. https://www.fastmail.help/hc/en-us/articles/1500000280221-How-Fastmail-provides-a-secure-service#contentsecurity