Email Attachments (winmail.dat attachments for PDFs)

Today I received attachments in the winmail.dat format. Someone was sending my PDFs and for some reason today, they aren't showing as PDFs. This is new and I know it works for other emails because I asked the person to send the attachment to another email address. Xfinity/Comcast, please look into this issue as I know it is due to something on your end (I've changed no settings and I've not had issues receiving attachments previously).