The recipient's mailbox is full

If you have sent a message to a Yandex address and received a non-delivery report that states the following: “Аccount is full”, “Error writing message: Disk quota exceeded”, “Inbox full”, “Over quota”, “Quota exceeded”, “Recipient's mailbox is full”, “User has exhausted allowed storage space”, this means that the recipient's mailbox is full and cannot accept your message. This usually happens because the recipient does not use their mailbox often and their mailbox is full.

Try contacting the recipient by another method and report the problem.