Questions

This could be due to a number of factors, usually temporary ones.
An email can follow a convoluted route.
If the destination server is not available (being too busy or for any other reason), your mail program will repeatedly attempt to deliver at specified intervals. If there in no success in a day or two the email will be returned to you as 'undeliverable'.
If your email was not returned, it means it was delivered somewhere ! (or it is still trying).