I recently encountered a very odd problem with YandexMail, which is my primary email client, and I do not find a lot of information about this problem online. It seems to be a configuration issue. Here is the error message:

Diagnostic-Code: X-Yandex; lost connection with mailsec.protonmail.ch[xxx.xxx.xxx.xxx] while performing the EHLO handshake

From what I gather, the issue is related to a configuration problem at Yandex, but as a mere consumer, I cannot fix it. I also never had a similar problem before. Anyway, if anyone of you needs to reach out to me via email and you use ProtonMail, perhaps send an email to my ProtonMail account (aaron.s.elias@…) and not my Yandex account.