Strange Outlook email problem “=smtp:”

As of today, I am recieving emails where the TO addresses come in as: =smtp:your@name.com rather than the normal your@name.com

When I hit reply or reply all, the messages do not get sent, as they are not recognized as legitimate addresses.

I can not find any help online at Microsoft, Google or other help sites.

Anyone have a clue what this is all about?

Thanks.