The Fix (for me)
If you have tried all other suggestions (see below), then try deleting your Outlook Autocomplete cache:
- Either 1 at a time by starting to type name with problems in the “To” field and then click the “X” against the address with the problem
- Or to delete the whole cache (the “to be completely sure” option!!) then: Outlook File tab, Options, Mail, Send Messages, Empty Auto-complete List
Why does this work?
There are lots of threads about emails sent from Outlook with an attachment (e.g. photo) being received by Mac Mail with the attachment replaced by a file called winmail.dat. And there are lots of places offering essentially the same answer as this very comprehensive one from Slipstick (http://www.slipstick.com/problems/outlook-is-sending-winmail-dat-attachments/). In summary you need to ensure that the sending format is NOT set to “rich text” in multiple locations:
- Specific contact card details for recipient
- General sending options in your outlook client
- Options on the Exchange server (inc O365)
- Etc etc
The suggestions here may fix the issue for you, however even after trying everything the problem was still there for me.
After the normal search, search and search again using different key words I came across a discussion about the Outlook Autocomplete cache and how this stores a snapshot of data about the contact separately. So I searched for a tool (http://www.nirsoft.net/utils/outlook_nk2_edit.html) that would allow me to read the internals of the .NZ2 file and see what data is stored. And as you can see from the results below there is a field “Sending Format”. After clearing the Autocomplete cache and trying to send again, viola the problem was resolved:
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