Hello. On October 5, Yandex stops supporting its Jabber-service, which allows you to instantly exchange messages via the XMPP protocol. All accounts associated with addresses on Yandex will become inactive. In order to continue to communicate over XMPP, create an account on another Jabber service. Unfortunately, the list of your contacts will not be saved, but the history of correspondence is most likely not going anywhere: if you had the corresponding setting enabled in the messenger, all messages remained on your computer. For any questions, feel free to write to the support service at online@support.yandex.ru
Source: https://habr.com/ru/post/397379/