I just tried to re-subscribe to the newsletter (to switch it over to another email address) but was unable to submit the form. The console said:
Refused to send form data to 'https://agilemail.createsend.com/t/r/s/btlddt/' because it violates the following Content Security Policy directive: "form-action 'self'".
This was on Chrome 68.0.3440.106 (64-bit) on macOS 10.13.6 (17G65).
I was able to subscribe successfully from Safari on iOS 11.4.1 (15G77).