This information needs to go in the mail.properties file, and if you edit this file via the admin page the settings aren’t saved, so you have to edit the file directly. This can be a little tricky when using Docker, which is one of the reasons why I don’t use it anymore.
No, but your Gmail account need to be set to “allow less secured applications”, so some people prefer to have a separate Gmail account.
Have you read and followed the instructions here:
https://github.com/blynkkk/blynk-server#enabling-mail-on-local-server
Not connected to this issue, but if you’re a Node-Red user then I’d suggest that you run MQTT code on your devices, and use Node-Red as the single bridge between Blynk and your network.
Pete.