Over the past three years, we have had an unofficial way of accepting Bitcoins which involved manually sending BTC to our Bitcoin donation address, and manually confirming the transaction with our support team to receive account credits. However, the general increase in the number of Bitcoin transactions over the years has made that approach unfeasible and made development of an automated system necessary.
We feel this is indicative of a broader trend, where the increased mainstream interest in Bitcoin will make it harder for merchants not to support Bitcoin, which will lead to more Bitcoin support, more transactions, and perhaps the continued appreciation of Bitcoin prices.
Ultimately, we believe having a more significant portion of our revenue via Bitcoin or other cryptocurrencies actually reduces our business risk, by providing more redundancy in the event of the failure of more traditional payment methods.
https://protonmail.com/blog/bitcoin-secure-email/