I can't comment on the above-accepted answer; hence, I am providing another answer.

Please note a few changes for the sample code to work in 2024.

1. connection string:
   • remove https:// as it is appended by the library.
   • remove the leading / at the end of the communication-server. It leads to the wrong auth header and results in 401.

example:

• connectionString := "endpoint=demo-communication-server.unitedstates.communication.azure.com;accesskey=your-access-key"

2. The Azure rest API requires attachments to be passed in even though you have no attachments. here is the updated payload that works.

payload: = emails.Payload {
  Headers: emails.Headers {
    ClientCorrelationID: "some-correlation-id",
    ClientCustomHeaderName: "some-custom-header",
  },
  SenderAddress: "<[email protected]>",
  Content: emails.Content {
    Subject: "Fabric tenant abcde wants to upgrade to paid offer",
    PlainText: "This is being generated from dev-server.",
    HTML: "<p>This is a <strong>test</strong> email.</p>",
  },
  Recipients: emails.Recipients {
    To: [] emails.ReplyTo {
      {
        Address: "[email protected]",
        DisplayName: "Garima Bathla",
      },
    },
  },
  Attachments: [] emails.Attachment {},
  UserEngagementTrackingDisabled: false,
}

3. The sender's email address needs to be in this format:

SenderAddress: "<[email protected]>",