doc(tem): indicates encryption is mandatory (#3840)

Author: cbouvat

managed-services/transactional-email/reference-content/smtp-configuration.mdx

@@ -35,7 +35,7 @@ Your Scaleway SMTP username is the Project ID of the Project in which the TEM do
 
 Your password is the secret key of the API key of the project used to manage your TEM domain. Follow this procedure to [generate API keys for API and SMTP sending with IAM](https://www.scaleway.com/en/docs/managed-services/transactional-email/how-to/generate-api-keys-for-tem-with-iam/).
 
-4 - **Encryption method** - If you want to encrypt the connection between your application and the SMTP server, there are usually two methods available:
+4 - **Encryption method** - An encrypted connection between your application and the SMTP server is **mandatory**, and two methods are available:
 
    - **SSL/TLS**: Also known as SMTPS, it allows you to directly define a secure connection on a secure port. Directly creates a secure connection on a port such as `465` and `2465`.
    - **STARTTLS**: This type will upgrade any insecure connections to secure connections on a non-secure port, such as 587.