Email Service Providers (ESPs) often restrict or do not support the use of <iframe> tags, including those used for embedding videos.<iframe> tags can potentially be used to execute malicious scripts or to embed harmful content. This poses a security risk both to the recipient and to the email system. By blocking <iframe>, ESPs help prevent phishing attacks and other security threats.
Embedding videos directly into emails can take control away from users who may prefer to decide whether to download or play a video. Forcing a video to load automatically, By forcing video to load automatically, can cause inconvenience to the users.