This is the list of all the possible reasons why yandex mail not sending email: 1. Weak Internet connection: Bad signal strength and weak internet are gonna cost the mail sending speed. So, opt for a good internet. 2. Plug ons: Remember that Yandex Mail is not compatible with plug ons, so disable them. 3. Antivirus Software: Sometimes, the protective software might diagnose it as a threat so you can try switching it off. 4. Loose physical cable connections: Check the cable connection wirings of the system that you are using. 5. Captcha loaded Browser: Make sure that your web browser is free of all the history and cache data.