"Accept All (Unverifiable)" is also known as a “catch-all.” This is a domain-wide setting where all emails on this domain will be reported as an accept all (unverifiable).
An accept all address is commonly used to ensure a company receives any email that has been sent to them, regardless of typos. Often times these are in-fact valid emails. However, some organisations may utilise this setting as a security feature to prevent unsolicited emails.