We received a call from the originating bank indicating that an incoming wire that was destined for our customer had been stopped as their customer's email had been hijacked and the wire wasn't authorized by their customer.
In speaking to our customer, it seems she fell victim to a Facebook scam. A FB friend, that she had never met, wanted to send her $18,430.00 to help her out. She was instructed to tell the bank, if asked, that it was for a mortgage loan.

Although the fraud was prevented, can we or should we file a SAR, even though the dollar threshold wasn't met?

Depending on if you want to waste your time or not. Unless you have some solid evidence that you think will assist law enforcement to catch the perps, it is probably a waste of time.

With the wire not being sent, why would the originating bank feel the need to notify your bank? I see no reason for you to spend another second on this, much less file a SAR.

Kind of what we were thinking but wanted to get other feedback! thanks!

A similar thing happend here. While a SAR was not needed, I did do a short write up and put this in my "SAR Not Filed" file just so the examiners would know that we did some due diligence.