Bounce error does not match with BriteVerify Results

When it comes to Marketo-emitted emails, always take Marketo's word for it at the same point in time. (And I say this as someone who operates a verification service!)

A few reasons for a non-Marketo service to succeed while Marketo fails:

• Marketo is sending a real email, while verification must stop before transmitting the body (so the 5xx could occur at the last step)
• The recipient's mailserver may specifically not want to receive mail from Marketo, so generates a response that's specific to the sending/testing IP
• The recipient may accept all mail and bounce it after the zero-hop (initial connection), called an "OOB bounce" by Marketo (this is unlikely to be the problem here, and represents an underlying server misconfiguration)

Not sure how BriteVerify is doing their verification but @aol, @yahoo, @verizon emails return as 'catch-all' addresses which means it can appear valid from a server-side scan but will bounce when a real email is sent.

There are some ways around it, but depending on your database size and audience it may or may not be worth it. Maybe check with BriteVerify on how they treat emails on those domains / if they can verify them.

100% agree with @Sanford Whiteman​. It's likely a point in time problem. If the email address bounced legitimately with a "not our customer" type of error, then was accepted at the time you tested with any validataion provider, that address may have been converted to a spam trap, which will again accept mail. If you're confident in the initial bounce categorization in Marketo for invalid, there's no need to attempt to re-validate those. We do a good job of classifying those that return verbose SMTP errors like this case "554 delivery error: dd This user doesn't have a aol.com account [-9] - mta4129.aol.mail.bf1.yahoo.com." There may be edge cases where you have configured a specific bounce like a Spam Block, Category 1 Hard Bounce to invalidate an address after multiple occurrences. That would not fall into this same scenario. I live and breathe Marketo bounce logs and I can say, we almost always have the invalids correctly classified.