(CBS) — A warning for everyone who uses an I-Pass for tollways: Beware what’s in your inbox.

CBS 2’s Chris Martinez reports.

When Barbara Christopher got an email saying she owed on her I-Pass, she figured that was possible. Then, she thought, “This probably is something to be suspicious about.”

She was right. It turns out the email was a scam, a classic email fraud targeting I-Pass customers.

The email warns of an overdue balance. Then sender is the E-ZPass collection agency, which looks like the real deal.

Fraud expert William Kresse says the scam is a convincing one.

“It’s something that’s credible, it’s something that doesn’t cost that much, and it’s a service that people need and are willing to pay for without questioning in order to keep that service operating,” he says.

A tollway spokesperson says officials know dozens of customers have received that email. They don’t know how many may have fallen for it.

They say they will only contact motorists about billing issues through the regular mail system, not by email.