From Interfolio:
"The envelope is a high-quality white windowed envelope through which the recipient address you specified is visible. Interfolio places one cover letter on top of your documents which explains the Interfolio service, who you are, and what we're sending on your behalf. It will also include the status of the documents in the package (whether they were received by Interfolio as confidential or non-confidential). If you started an account through one of our partner institutions the cover letter will have the school's logo rather than Interfolio's. In the future, we will have a preview option that will allow you to see these cover letters before submitting your request, so that you have some idea of what it looks like.Interfolio Support"