https://www.winmailviewer.com/terms
The #1 iOS app to open winmail.dat files instantly. Extract all Outlook attachments, documents, and images from TNEF files. 100% secure, works offline....
file vieweropendatfilesiphone
https://www.laptopmag.com/articles/stop-outlook-sending-winmail-dat-file-email-attachment
Prevent Outlook from attaching strange files, called winmail.dat, to your messages.
dat filestopoutlooksending