What are reasons that emails could be "delivered" but not received?

[Anonymous]

We have had several cases recently where outreach to clients was reported as never having been received. The clients also claim that they checked their spam folders and did not see the email in there.

However, after looking into the details of the activity log of some of these clients, Marketo thinks the emails have been successfully delivered (albeit not opened). Are there cases where Marketo will receive confirmation from the destination mailserver that the message was received successfully, but that some sort of filtering mechanism after the fact would prevent it from reaching the client inbox?

Or are we dealing with people who probably got the email but just missed it?

[SanfordWhiteman · Accepted solution]

As you've correctly divined, if an email with a Delivered activity (and no subsequent Bounce activity) never arrives in an inbox, that means it's been summarily dumped by an anti-spam layer that doesn't even care to give feedback to the sending server.  It's something we see, for example, when domains have blacklisted Marketo IPs and/or envelope senders because marketing email is broadly prohibited by company policy, regardless of individual end-user interest. 

Another possibility is you've messed up your DKIM config or have another major DNS issue (like sending from a domain that does not exist) and the recipient server is unfortunately unable to reject the email at envelope time (envelope = initial connection), but they dump it as soon as they realize how bad it looks.

Silently deleting mail is about the harshest treatment anti-spam software can dish out.  You should try to reach out to their IT next.

[Anonymous]

Hi Stanford, I've also seen that people from the same company, same location get different delivery results. Some can receive but some cannot even though it marked Delivered in Marketo. How would this happen?

Thanks!

[Anonymous]

Thanks for the confirmation and clarifications Sanford.

[Robb_Barrett]

Don't forget that if the email browser has auto download of images turned off there will never be a response to the server that the email is opened. This used to be the default for a while but it's reverted back, however some organization may still ask the recipient to approve the sender. Your email might have been viewed but the view not recorded.

That's not the answer to this question, as you've given a clear case where the recipient has confirmed it's missing.  We've had this happen as well and it turns out the organization blacklisted the address. The email doesn't get outright rejected from the mail server, it's delivered to the server and then not delivered to the recipient.