While .mp4 files themselves are generally safe, you should remain cautious of files from unknown sources:
: You can play this file using standard media players such as VLC, Windows Media Player, or QuickTime. Cloudmail (3) mp4
: Likely an attachment from a webmail client (like Gmail or Outlook) or a file shared via a cloud service (like Google Drive or Dropbox). The "(3)" in the filename usually indicates that
A file named is typically a video file downloaded from a web-based email service or a cloud storage provider. The "(3)" in the filename usually indicates that it is the fourth copy of that specific file downloaded to your device, as operating systems automatically rename duplicates to avoid overwriting existing files. File Characteristics Windows Media Player
: .mp4 is a standard digital multimedia container format most commonly used to store video and audio.