A video file that is long is often too big. Many e-mail servers, networks or website clients won't allow you to send messages that are too big for their system. If you wish to send someone a video, and the video is too big or too long to send via e-mail, there are a few ways that you can change the video in order to send it, or at least to get the video to the person who needs to see it.
Compress the video. Place it in a folder and right click on the folder. Choose "Send to" and then "zip file" to send the video in the folder to a zipped or compressed file. Then, try attaching the video to your e-mail again and see if its small enough.
Open the video in video-editing software, if you have any on your computer. Cut the video into pieces and save them as separate videos. Then attach each of them, one at a time, to e-mails to send them to the receiver.
Host the video at a video hosting site online. There are hundreds of sites, some listed in Resources, where you can upload a file for free. Then, you can send the person who was to receive the video a link to the place where the video is hosted and in many cases a password to access the file. This will allow them to see or download the video without you sending it via e-mail.