It obviously makes no sense to block the mail system if you disagree with some of the letters sent. The deceptive method of blocking used here, targeting the back-end servers so that mail traffic simply gets ignored, while Russian Protonmail users still seemingly can access the service, is another sign that they’d rather not let you know blocking goes on at all. This is an action against end-to-end encryption.
The obvious answer is to use more end-to-end encryption, and so increase the cost of surveillance and repression. Use my protonmail address as listed on the right, or use PGP using my public key on the right to contact me. Other means of reaching me with end-to-end encryption are the messaging apps Signal and Threema, as well as Keybase (listed on the right as well).