Hello @NOREENH7 ,
.mp4 files can't be uploaded into the Library, nor embedded into emails sent through us. If you're trying to insert a video or audio mp4 into your email, we'd recommend hosting that on a video/audio-hosting site or cloud service, then inserting its share link into the email. If you're trying to insert a still image .mp4, then we'd recommend converting that to a .jpg or .png file, and then upload that to the Library / insert into your email as normal.
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