Notes users receive messages with winmail.dat attachments. This occurs even though TNEFEnableConversion=1 is enabled on the Domino SMTP server.
From the TN 1441039
This issue is fixed in Notes/Domino 8.0.2 FP6, 8.5.1FP3 and 8.5.2.
Fix details: SPR# SAZR7V3ME6