Message Regarding the ProtonMail DDoS Attacks - ProtonMail Blog
protonmail.com/blog/protonmail-ddos-attacks
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
We are happy to announce today that after several days of intense work, we have largely mitigated the DDoS attacks against us. These attacks took ProtonMail offline making it impossible to access emails, but did not breach our security. At present, attacks are continuing, but they are no longer capable of knocking ProtonMail offline for extended periods of time. As our infrastructure recovers over the next several days, there may still be intermittent service interruptions, but we have now largely restored all services. Our successful recovery was only possible due to the valiant efforts of IP-Max and Radware, and we would like to sincerely thank them.