Outlook: duplicate emails in Sent folder

Outlook: duplicate emails in Sent folder

This appears to be recent behavior:  When I send a message from Outlook using the Zoho SMTP, I am getting duplicates in my "Sent" folder. 

After noticing it, I tried sending messages to another of my email address and saw that while I ma getting duplicates in my Zoho Sent folder, the system is not sending duplicate emails to the recipient.

What's up?