Email Deliverability

How does email work

When a sender creates and deploys an email (typically through their email service provider, or ESP), it is transferred from server to server via the Simple Transfer Mail Protocol (SMTP). To determine the destination email address, the SMTP contacts the DNS server and checks whether that domain has any mail exchange servers with information about where the message should be sent.

Once the SMTP has confirmed the destination, it transfers the message to the email recipient’s Mail Transfer Agent (MTA) server, commonly hosted by an Internet Service Provider (ISP, also known as a mailbox provider, or MBP) such as Gmail, Microsoft, and Yahoo. Before the email reaches the ISPs’ server, additional checks are run on the sender’s authentication, IP and Domain reputation, and infrastructure to ensure they are safe and can be trusted.
Once the email has successfully made it through the MBP’s gateway, it is considered delivered. The sender’s reputation and subscriber engagement history will determine whether the mail will land in the inbox or spam folder. The inbox placement rate is based on the number of messages that reached the inbox.

~20% of sent mail is not reaching recipients’ inboxes.

A high inbox placement rate is determined by the health of an email program. This health relies on adherence to email best practices like list hygiene, content evaluation, and engagement, but infrastructure and authentication also play a significant role in an email program’s success

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Infrastructure

Email authentication

Sender Policy Framework (SPF)

DomainKeys Identified Mail (DKIM)

Domain-based Message Authentication, Reporting & Conformance (DMARC)

DMARC addresses exact-domain spoofing and phishing attacks by preventing unauthorized use of a domain in the “From” address of email messages. DMARC is quite different from the other authentication methods. It is a framework that sits atop SPF and DKIM authentication, rather than working in silo alongside it. DMARC allows the sender to specify how unauthenticated or non-compliant messages should be treated by MBPs. It helps mail administrators prevent hackers and other attackers from spoofing their organization and domain.

The true beauty of DMARC protection lies in the three available policies which allow senders to instruct the MBPs on how to treat unauthenticated mail. The three options are:

• Policy is ‘none’ (p=none): MBPs will take no action and deliver the mail as normal
• Policy is ‘quarantine’ (p=quarantine): MBPs will send the message to spam/junk
• Policy is ‘reject’ (p=reject): MBPs will drop the message and it will not be delivered to recipients

Email deliverability best practices

Sender reputation

Sender reputation is how MBPs measure the trustworthiness of an email program. MBPs use sender reputation to determine if emails should be delivered to the inbox, the spam folder, or blocked completely. A poor sender reputation results in fewer emails delivered to your subscribers’ inbox, which can reduce conversions and, ultimately, ROI. There are two key factors of sender reputation:

• Engagement: Engagement describes subscriber activity with email, which may be positive or negative.
• Positive engagement includes rescuing email from the spam folder or marking it as not junk, opening or clicking on the email, or moving the message into a folder.
• Negative engagement includes actions like marking the email as spam or junk (also referred to as a spam complaint, and the number one reason for declining sender reputation), deleting the email without opening, or never reading the email at all.
• List hygiene: Sending to bad email addresses indicates that a sender is employing risky acquisition practices and isn’t sending to subscribers who signed up to receive their emails

List hygiene

List hygiene is a process of data validation undertaken by email marketing teams to ensure that they have a clean email list comprised of valid and positively engaged subscribers. A successful email program is closely tied to having healthy email lists, as list hygiene is a top priority for MBPs. There are three types of bad email addresses to avoid in order to maintain a clean email list:

• Unknown users: Unknown users are invalid or unrecognized email addresses in a sender’s database. Examples of unknown users include email addresses that have been abandoned and shut down by the MBP, or email addresses that have been mistyped or malformed and are therefore not actual email addresses.
• Recycled spam traps: Recycled spam traps, sometimes called repurposed spam traps, are addresses that were at one time legitimate destination addresses that have been repurposed to catch abusive mail.
• Pristine spam traps: Pristine spam traps, also referred to as true traps or honeypots, are email addresses created solely to capture spammers. These email addresses were never used as legitimate email addresses, do not subscribe to email programs, and do not make purchases.

Sending to these types of email addresses negatively impacts sender reputation and the chances of an email making it past the gateway and into the inbox. Blocklists, which also contribute to a sender’s reputation, monitor spam trap activity to catch any senders that have poor email address acquisition practices.

Schedule and consistency

Segmentation and personalization

Brand recognition

“We are clear there’s a straight-line relationship between better inbox placement performance and Philips’ program revenue. We also now have a deep understanding of what affects our deliverability and why, which has improved our engagement levels significantly.”

– Charlie Wijen – Digital and CRM Specialist, Philips

Conclusion