Hello,
I checked this feature myself and it works for me. First, try resetting the router to factory settings. Check if your firmware is up to date, if not, then update:
https://wiki.teltonika.lt/view/RUT9xx_Firmware
Also, make sure that the email you use has no restrictions on connecting to third-party devices. For example, if you use Google gmail then you need to enable third-party access in your mail settings. If the issue persists, generate the troubleshoot file and send it to me via private message.