If someone missed one or more of the emails in an auto-campaign, or you wanted to send an email associated with an auto-campaign to a contact who isn't in the campaign, you definitely can!
From the auto-campaign, click on the campaign email that you would like to send.
Now, click Quick Send and choose the contact you wish to send it to.
If you use Quick Send, it will add the individual to the exclusion list meaning if they end up in the campaign they will not receive it again
If the person already received this email and are intentionally sending it again, it will be sent.