Accept-all is also known as an “Catch-all”, is a domain-wide setting where all emails on this domain will be reported as a catch-all. There is no definitive way to determine whether this email is valid or not.
The risks of catch-all emails
Increased Bounce Rate – Unpredictable bounces are the biggest risk to your sender reputation and the main reason to be extremely cautious. Catch-all mailboxes frequently go over their quotas, resulting in additional bounces.
But using below trick, you can easily verify 50% or more of your accept all emails.
Please note that this method works to verify emails that are using google as ESP but still better than losing all your accept all emails.