Hi @Jorge Acevedo ,
According to my research, the "winmail.dat" file format is often created by Microsoft Outlook when it sends emails in the Rich Text Format (RTF). If you're using Outlook, you can change the email format to HTML or Plain Text to prevent winmail.dat files from being sent. Go to File > Options > Mail > Compose messages and select HTML or Plain Text under the Compose messages in this format dropdown.
More information, you can refer to the How message format affects email messages
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