Can you solve Smartsheet / Email problem?

I use Smartsheet to run my business. There are five people who work on this with me. About 6 weeks ago some of the notifications coming through to my email started flagging up as a message from Elizabeth, and now everything comes through as from Elizabeth. So if Henry sends me a message from Smartsheet it arrives as "Elizabeth via Smartsheet" instead of "Henry via Smartsheet." Elizabeth hasn't worked for us for nearly two years and is no longer a registered user of my Smartsheet. In face I can't find any trace of Elizabeth in the Smartsheet admin or users. Is this something Smartsheet had started doing or is my email system flagging every incoming email as from Elizabeth? What is going on and how can I change this back to what it should be?

I use a MacBook Air and Mail.