What is the correct way to upload an attachment before sending an email via the Zimbra SOAP API?

Upload the attachment using `FileUploadServlet` at `https://<server>/service/upload?fmt=raw,extended`. Include the file in a POST request with a `Cookie` header containing the auth token. The response returns an `aid` (server attachment ID) and file type. This attachment ID is then used in the `SendMsg` command. For full details, refer to the Zimbra SOAP API Development Guide 3 - Email Operations and the related Zimbra SOAP API Development Guide 5 - Email Forwarding for advanced email operations.