Ever wonder why two envelopes are used to mail a formal invitation? Here's the answer.
Hand delivery was once considered the only correct formal way of delivering a message. Footman were employed for the task. When footmen were in short supply, they had to resort to the public post. The real message was addressed as before with only the name of the recipient on the inner envelope and the mailing address on the outer envelope. And that is why two envelopes are used for formal invitations to this very day.