If you use an email service provider, you most likely have tracking reports that tell you the disposition of each message you send. These reports usually indicate the message falls into the broad categories of “delivered” or “bounced“. While many ESPs use more detailed categories, you just want to see if your email made it to the recipient or not…right?

Of course. So what happens when you send out that nice shiny new email and you get a response rate far lower than what you were expecting? Naturally, you check in with some of your best recipients to make sure they got the message. Your tracking shows delivered, but when you reach out they say they didn’t see the message at all. Not in the inbox. Not in the spam folder. Not even in quarantine…now what?

Why is your ESP telling you the message was delivered when it clearly wasn’t?

To answer this common question, let’s dive a bit deeper into what that “delivered” status really means.

When you hit the Send button at your ESP, your mail server will attempt to hand off your message to the mail servers for each recipient. The initial contact between the sending mail server (your ESP) and the receiving mail server (your recipient’s email provider) is often referred to as the “handshake.”

At the time of this handshake, the ESP server will attempt to hand off the message to the receiving server. When this happens, there are a few potential outcomes:

1. The receiving mail server rejects the message due to the address not existing, the sender being blocked, or other errors considered permanent. These are hard bounces, and usually the receiving server returns a code in the format 5xy, where x and y are additional digits that indicate the specific type of hard bounce. This error typically causes a bounced status in your ESP reporting.
2. The receiving mail server returns a temporary bounce or deferral. These bounces indicate the mail cannot be delivered at this time, but the sending server should try again later. These are soft bounces, and are typically accompanied by a 4xy error code. These can generate a bounced status in your ESP reporting if the subsequent delivery attempts are not successful. If the later sends do make it through, these will show as delivered. 
3. The receiving mail server accepts the message for delivery. This is considered a successful delivery, and is accompanied by the code 250 OK. These are reported by your ESP as delivered. 

Once this handoff takes place, the sending server (your ESP) has no further visibility into the delivery of the message. There could be additional spam filters in place after the message is accepted, or individual user settings could cause the message not to be delivered, with no further notification to the sender.

While it’s not extremely common, even major ISPs have been known to have messages “dropped on the floor” if the sender’s reputation is not up to their standards. This is the (highly technical) term for a message that is accepted by the receiving server, but then essentially disappears. It’s not returned to the sender, but it’s also not delivered to the recipient’s inbox or spam folder. It’s simply deleted.

So how do you find out what really happened?

That can be the tricky part. Since the information is not shared with the sender or ESP, the only way to find out for sure what happened to one of these messages is to check the mail logs for the receiving server. In most cases, this will require working with IT staff on the recipient’s side who can search for the message(s) in question and provide a definitive answer on what happened to the message and why.

If the recipient’s IT team isn’t an option, you can also check the content of your message, as well as the reputation of your domain and the domains of any links within the message body. In many cases the initial handoff looks primarily at the reputation of the mail server (IP address), while the subsequent filters can include message content, link URLs, domain reputation, and other factors.

Check out the Resources page for links to some of the most popular reputation tools, and feel free to comment with any additional questions.

– BG