Old comcastbiz.net email is still active?

I work for a business that transferred ownership in 2023. The old owner had a comcastbiz.net email, that was supposedly shut down. When I started working here in late 2024, I noticed on the office Mac that we were still receiving mail to that email address through the Mail app. I thought maybe I got confused with our current email (hosted by Google), but I certainly never connected it, and there were non-marketing non-spam emails from real clients that were showing up in the Mail app that were not in our current email. I finally was able to speak with the old owner a little this week, who was certain service was shut down. They gave me the login information for the Comcast Business account, but when I login, I can't do anything, because it says our service is discontinued and has been for a while now. I'm a little concerned because it looks like the connection to Mail was severed as no new mail has showed up in the app since March 2025, but when I send an email to the old address, it doesn't bounce. How do I verify that this email is shut down for good? I want to make sure that our customers with our old address don't try to contact us but don't get a bounce!