How Sender Reputation Impacts Inbox Placement

Email marketing and deliverability experts agree that sender reputation is the most important factor that determines where an email lands: Inbox or Spam. You start building your sender reputation from the point when you start sending email messages from the domain. And the way how you do it determines how good or bad the reputation will be.

In this article, we will give some background about an email delivery process, help you understand the difference between delivery and deliverability, and give recommendations on how you can proactively monitor your domain reputation to make sure you have a good one.

Delivery vs Deliverability

The process of transmitting an email from the sender to the recipient can be divided into two parts:

1. The first part is called ‘Delivery’ and refers to whether the message was accepted for delivery to the target recipient or rejected. The sending server sends the message. When the message reaches the receiving server, the server verifies the authentication of the sender and looks if the recipient’s mailbox exists or not. If the sender is authenticated and the recipient’s mailbox exists, it accepts the message for delivery. If the sender is not who it claims to be, the message can be rejected. And if the recipient’s mailbox is not valid, the message is bounced back.

2. The second part is called ‘Deliverability’ and refers to where the message is placed after it is accepted for delivery. Inbound emails get sorted and land either in the Inbox or Junk folder depending on several factors that mailbox providers look at. Each mailbox provider develops its mechanism of email sorting based on the resources it has in place.

The technical aspects involved in an email delivery process are:

1. IP Address.

When we are talking about email sending, the IP of the SMTP server or email service provider is taken into account. This IP address is for the machines (receiving servers). The recipients don’t see the IP address the email originates from when they read the email in the Inbox.

The IP address can be shared or dedicated. When it’s shared, it means that many senders are sending from the IP or a pool of IP addresses. Email service providers typically send emails for their customers from pools of shared IP addresses. A dedicated IP address means that only one sender is sending emails from that IP.

Read more: Dedicated vs Shared IPs: Which Should You Choose for Better Deliverability

2. Mail FROM/Envelope-From/Return-Path Email Address.

It is a complicated email address that indicates where the message must be returned in case it’s not delivered. The ‘Mail FROM’ email address is also for machines. Typically, email service providers use a ‘Mail FROM’ email address set up on their domain. Some ESPs, however, allow customers to customize the domain for ‘Mail FROM’ by adding a DNS record for the domain.
The ‘Mail FROM’ or ‘Return-Path’ email address can be seen in the message headers.

3. ‘From’ Email Address.

This email address is for humans. It is an email address that the recipients see in the ‘To’ field when they find the email in their mailbox. Companies sending emails normally use a friendly ‘From’ email address set up on the company’s domain or subdomain that facilitates brand recognition.

Let’s see how the above three components play out together in the delivery process.

When you click the ‘Send’ button, your email service provider starts a conversation with the receiver’s server. The receiver’s server looks at the IP address, ‘Mail FROM’ domain, and ‘From’ email domain and makes the decision about the email. The main things that the receiver’s server takes into account are:

1. Reputation.

If the IP reputation is good, the server accepts the message for delivery. Now the domain reputation makes the difference where the message is placed.

If the IP reputation looks suspicious, the server may greylist the message and say “Please, try again later” or throttle the message delivery.

If the IP reputation is poor, the server can end the conversation and bounce the message back or block it without a bounce.

2. Authentication.

The receiving server checks the originating IP address, ‘Mail FROM’ domain, and ‘From’ email domain to make sure that the message is coming from the sender it claims to be from. It checks whether or not the message is authenticated with SPF and DKIM and whether or not it passes DMARC.

If the message fails SPF and/or DKIM check, it is subject to more filters, and in most cases, the message is placed in the Junk folder.

If the message passes SPF and DKIM checks but fails DMARC, it depends on the DMARC policy what will happen to the message: delivered in Inbox, delivered in Junk, or blocked.

If the message passes the DMARC check, the email receiver decides its placement based on other rules or filters it has in place. Such a message has a good chance to land in the Inbox.

Read more: Email Authentication: Ultimate Guide

You may be asking yourself: why should I spend time trying to understand how the email delivery process works and all those things related to it?

The good reason for it is that when you are sending an email, you are not the only person who is sending the email to that particular server at that time. You are only one of the hundreds of thousands, if not millions, of senders who are sending emails to the receiving server. The server is filtering millions of emails because it only wants good and safe messages to get through. Unwanted, suspicious, and malicious emails will be blocked.

How is the server doing it? It is looking at hundreds of different factors, unique identifiers, in the emails that are coming from the sender. It tries to build up a history of what it has seen and this is what is called sender reputation.

The unique identifiers that make up sender reputation are:

IP Reputation:

• Shared IP or dedicated IP;
• Reported spam

Domain Reputation:

• ‘Mail FROM’ domain (the ESP’s domain or customized sender’s domain);
• ‘From’ domain (sender’s domain);
• Reply-To email address;
• URLs used in the messages including ‘View in browser’ and ‘Unsubscribe’ links;
• Tracking links;
• Email authentication (SPF, DKIM, and DMARC);
• User engagement (spam/not spam markings).

Because more data points are used to create a domain reputation, it is more impactful on deliverability than an IP address reputation. This is not to say that an IP reputation is not important. It absolutely is. The IP address is the first thing that the receiving server sees. And if its reputation is not good, the conversation with the sending server may not happen. When it’s good, the message is accepted for delivery, and where it will be placed is dictated by the domain reputation.

How to Monitor and Keep Good Sender Reputation

Read the full story at GlockApps blog.