Undo "Delayed Send"?

I just sent out an eMail via the “Delayed Send” feature.
However, I would actually like to prevent the mail to be sent at the date that I designated (the day after tomorrow).
I cannot find the message anywhere though, so how do I do this? Is it even possible without completely uninstall em Client? (Because I guess it can’t delayed send when I uninstall it, right?!)

Delayed send items remain in the Outbox until they are sent.  The Outbox is a local folder, so either have local folders displayed or right-click on any folder in the Smart Folder section and select Display and then make sure “Outbox” is checked.  I have not spent a lot of time with delayed sends, but I do note that if you open the message and select “Delayed Send”, you can change the send time to before the current time and it will send immediately.