To use SendGrid or any other SMTP server with Ory Kratos, you need to provide the SMTP server details in the Kratos configuration file. The error you're seeing indicates that the

courier.smtp.connection_uri

property is missing in your configuration. Here is an example of how you can set it up:

yaml courier:    smtp:    connection_uri: <smtp://username:password@server:port/>

Replace

username:password@server:port/

with your SendGrid SMTP server details. If you're using AWS SES SMTP interface, you can also configure custom SMTP headers for cross-account sending:

yaml courier:    smtp:    headers:    X-SES-SOURCE-ARN: arn:aws:ses:us-west-2:123456789012:identity/example.com    X-SES-FROM-ARN: arn:aws:ses:us-west-2:123456789012:identity/example.com    X-SES-RETURN-PATH-ARN: arn:aws:ses:us-west-2:123456789012:identity/example.com

If your SMTP server requires a unique identifier for the HELO/EHLO command, you can configure the identifier:

yaml courier:    smtp:    local_name: <http://exmaple.org|exmaple.org>

If your SMTP server enforces certificate-based authentication, you can configure the client certificate and client private key:

yaml courier:    smtp:    client_cert_path: /somepath/client.cert    client_key_path: /somepath/client.key

Please refer to the [Ory Kratos documentation](https://www.ory.sh/docs/kratos/self-hosted/mail-courier-selfhosted) for more details.