What is the error and why does this happen?

Error: cldfs.CloudFilesException: {"message":"Email not verified","error":"Unauthorized","statusCode":401}

This is a security check enforced by CloudFiles to ensure that the connecting Salesforce user's email is verified. It happens only in sandbox environments as Salesforce wouldn't allow you to create a production user without email verification.

How to fix this issue?

To resolve the error, you simply need to verify your email address in Salesforce:

  1. Log in to Salesforce with the user facing the error
  2. Go to your user settings by clicking your avatar > Settings
  3. Click Personal Information
  4. Next to your email address, click Verify (if available)
  5. Check your email inbox and complete the verification link

Refer the Salesforce article for more information to Verify User Email Addresses.