Whats with the RASH of Multiple emails being sent out by Outlook here of late?

I have several of my customers that use M$ Outlook is sending multiple emails out of the same email

I am getting support tickets thinking its the IW server causing the problem when in reality the email header is showing that the customer is actually sending using their local ISP’s SMTP server, thus the IW SMTP server isn’t even in the equation.

So for my wifes PC has had this problem and I have had 3 other clients that has had this issue.

Have any of you had this issue or been reported to you?