proof that emails was indeed sent to the supplier

Hi,

We’re facing a situation where suppliers claim that when their registration is rejected or they receive a resubmission request, they don’t get an email notification.

I tested these scenarios , and it appears that the email is sent.

However, I couldn’t find a clear proof in the BPM history to show that the notification was triggered.
Is there any way we can confirm or present evidence that the email was indeed sent to the supplier?

Thanks,
Shira

Code Snippet (add any code snippets that support your topic, if applicable):