There are some fundamental differences between copying an email, resending an email, and resending an email through QuickSend. See below:

1. You will Copy an email to make content changes to the message (such as dates, offer information, corrections, etc.) so that you can send it to a new list or to the same list again.
2. You will Resend an email (as is, with no edits capable of being made) to new contacts, those who have joined a contact list after the original campaign was sent.
3. You will Quicksend an email (which cannot be edited and is sent unchanged, as when resending) when you want to send it to individual contacts from other lists.