Google often-times makes severe algorithm changes. There is an SEO company called MOZ that keeps track of these. If you see right around the same time that ProtonMail suffered a disruption of rankings they were in the middle of a huge update (https://moz.com/google-algorithm-change). This was May 10th of this year.
I also want to say I'm not a Google employee and have no vested interest in the authenticity in their algorithm.
It is very fishy that according to PM they contacted a Google rep via twitter and got a "we fixed something" response from them.
As an SEO person, my opinion is this:
As an encrypted email service ProtonMail probably gets a lot of foreign and otherwise "undesirable" (or deplorable ;) ) links in the eyes of Google. Google lately has been doing a lot of algorithmic changes to actively sift these types of links out of consideration when ranking sites or dampening them severely.
My guess is that Google was basically penalizing PM for the links they were getting without notifying them via Webmaster Tools. Whether or not there was a manual penalty involved that they weren't notified about also adds a little bit of shadiness. Maybe Google thought PM was trying to game the algorithm or at the very least many of the links they were getting were of a spammy nature and they ran a penalty on them.
The redirect from them changing a domain in the past can also compound issues with Google. Sometimes they consider redirects spammy depending on what kind of redirect is in place.
Without more info it does seem weird that they would "fix" something not only without warning them in the first place but not explaining it afterwards? Most web admins have to use what's called a "disavow" list to remove the penalized links but apparently their rep seemed to do this for them. Probably due to the anti-trusty viral nature of the complaint?
I don't know what SERP tracker PM is using for these stats. Barring there were no errors in that system, they can trace the lack of rankings to a lack of organic traffic, and they were given no reasoning to the penalty or what was going on...
They may want to hire a lawyer and start an anti-trust suit on Google. This is very fishy without any official information from Google.
Thats interesting it would be interesting to look at there link profile - getting out of a link penalty is hard it took me over a year to get on client out of one.
I am referencing the official ProtonMail blog post (https://protonmail.com/blog/search-risk-google/) linked by another commenter in this thread.
I also want to say I'm not a Google employee and have no vested interest in the authenticity in their algorithm.
It is very fishy that according to PM they contacted a Google rep via twitter and got a "we fixed something" response from them.
As an SEO person, my opinion is this:
As an encrypted email service ProtonMail probably gets a lot of foreign and otherwise "undesirable" (or deplorable ;) ) links in the eyes of Google. Google lately has been doing a lot of algorithmic changes to actively sift these types of links out of consideration when ranking sites or dampening them severely.
My guess is that Google was basically penalizing PM for the links they were getting without notifying them via Webmaster Tools. Whether or not there was a manual penalty involved that they weren't notified about also adds a little bit of shadiness. Maybe Google thought PM was trying to game the algorithm or at the very least many of the links they were getting were of a spammy nature and they ran a penalty on them.
The redirect from them changing a domain in the past can also compound issues with Google. Sometimes they consider redirects spammy depending on what kind of redirect is in place.
Without more info it does seem weird that they would "fix" something not only without warning them in the first place but not explaining it afterwards? Most web admins have to use what's called a "disavow" list to remove the penalized links but apparently their rep seemed to do this for them. Probably due to the anti-trusty viral nature of the complaint?
I don't know what SERP tracker PM is using for these stats. Barring there were no errors in that system, they can trace the lack of rankings to a lack of organic traffic, and they were given no reasoning to the penalty or what was going on...
They may want to hire a lawyer and start an anti-trust suit on Google. This is very fishy without any official information from Google.