Installing Redash is straightforward if you use https://github.com/getredash/setup repository. Just run setup script to download, install and configure all required packages. But there is one thing missing from the default. It is mail configuration. First install Redash with all default settings and then edit /opt/redash/env file:

REDASH_MAIL_SERVER
REDASH_MAIL_PORT
REDASH_MAIL_USERNAME
REDASH_MAIL_PASSWORD
REDASH_MAIL_DEFAULT_SENDER
REDASH_USE_TLS = true
REDASH_USE_SSL = false
REDASH_HOST

After setting those values run docker-compose up -d command to recreate containers. Use TLS and local IP address if you host your mail server on-premise. Now you should be able to send mail messages from your Redash.