Email Deliverability Cheatsheet

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*Updated in September 2024

What is Email Deliverability?

Email deliverability is the ability of an email message to reach the intended recipient’s inbox, which is affected by spam filters, client-side filters and junk folders. It refers to the rate of success of in being delivered and filtered to the inbox, where the recipient does not report the email as spam or unsubscribe. It also refers to the management, procedures and technologies surrounding this process.

Coding for Email Deliverability

• Make sure to use clean and efficient HTML. Properly close HTML tags to avoid undesirable email rendering.
• Don’t embed CSS in header tags, as many email clients strip these tags from the email.
• Use an HTML validator to guarantee your message uses correct HTML.
• Include a text version along with the HTML version to ensure readability from clients that can’t receive HTML messages.

Subscription Best Practices

• Sign up for ISP feedback programs when offered.
• Use the highest permission standard you can support, such as double opt-in. At a minimum, send bulk mail only to contacts who have provided 1^st party permission. As a reminder, Adobe’s Acceptable Use Policy requires 1^st party permission for any contact used in a bulk email send.
• Provide subscribers with detailed sign-up options so they have a clear idea of what they will receive and the frequency they will receive it. Some new subscribers drive complaints because they are not receiving the content they wanted/expected or are receiving too many messages.
• Honor a recipient’s unsubscribe, even when moving to a new email service provider.

Glossary Terms

Authentication – Technical standards through which ISPs and other mail gateway administrators can establish the true identity of an email sender.

Blocklist – A list of IP addresses or domains believed to send spam

Bounce – A message that is returned to the sender because it was not deliverable

Cascading Style Sheet (CSS) – Controls the design and format of a document written in HTML

Deliverability – The ability of an email message or campaign to reach the intended recipient’s inbox, which is affected by sender reputation, ISP filters, client-side filters and additional security systems

Delivery Status Notification (DSN) – Also known as “bounce message”, a system that informs the sender of a delivery problem

DKIM (DomainKeys Identified Mail)– A method for email authentication that allows an organization to take responsibility for a message in a way that can be validated by a recipient server

DMARC (Domain-based Message Authentication, Reporting & Conformance) - authentication protocol that allows you (the domain owner) to specify how mail that does not pass SPF or DKIM should be handled

DNS Records – The database records stored in a domain’s name system

Domain-based Message Authentication, Reporting & Conformance (DMARC

Domain Name System – A naming system for computers connected to the Internet or private network

Email Service Provider (ESP) – A company that provides email services, including batch email and email marketing

Feedback Loop –A mechanism for an ISP to forward complaints of recipients to the organization that sent the email

Internet Protocol Address (IP Address) – A number assigned to each computer or network in order to distinguish each network interface and networked device

Internet Service Provider (ISP) – Sometimes referred to as Internet access provider (IAP), gives customers access to the Internet and may also provide mailbox services

List Fatigue – A condition producing diminishing returns from a mailing list whose members are over messaged

Phishing – Sending email that claims to be from a legitimate organization to trick recipients into providing personal information

Role Accounts – An email account that is associated with a department, office, position or task that is commonly in use by by more than one person

Seed List Addresses – Email addresses maintained by a deliverability provider that have the ability to report on how a message was filtered following delivery

SPF (Sender Policy Framework) – Authentication protocol that allows a domain owner to specify which IP addresses may send mail from the domain.

Spam Traps – Email addresses that are in use by blocklisting providers and other anti spam systems to identify problematic sending IPs and domains

Spoofing – A fraudulent email activity in which the sender address and email header are changed to look as though the email originated from a different source

Design for Deliverability

• Don’t embed your text and graphics in a single image. The email should not contain attachments or large images.
• Check to see how your email will render in each ISP.  Address rendering issues before sending.
• Use “absolute” links. Be sure to code your links so the email client can recognize where it is going.
• Do not link images used elsewhere. Because of human error, it’s best to not use images that are linked somewhere else on your website.

Top Data Measured by ISPs

• Volume: Email bad actors are more likely to send high volumes of mail. If your company has a high volume of email, make sure your complaint, hard bounce and spam trap hit rates are low.  If you are a dedicated sender, ensure your mail volume is consistent and predictable, and avoid unexpected rises in volume.
• Complaint rates: This is the amount of times email recipients hit “report spam” when they receive your emails. Small increases or decreases can dramatically affect your inbox performance.  Note that not all spam complaints will be shared by ISPs, and some ISPs will never share spam complainers.
• Bounce rate: A bounce is a rejection by the recipient’s mail server, and bounces can occur for a wide variety of reasons.  Reviewing the text details returned with a bounce can be helpful in understanding why the message was rejected.
• Spam trap addresses: Spam traps are email addresses that are used by blocklisting and deliverability providers to identify problematic senders.  These addresses have never been or are no longer in use by human recipients.  Inadvertently sending to spam trap addresses can cause a sending IP or domain to be blocklisted, which may result in delivery failures.  Poor list hygiene leads to inclusion of spam trap addresses on a mailing list.
• Authentication: Authentication lets the ISP know that the sender is who they say they are.  Authentication standards include SPF, DKIM and DMARC.

How to Keep Your Lists Clean

• Learn how your server processes bounces. Regularly clear out role accounts, clearly non-used addresses and addresses with errors.  Create programs to address contacts that chronically soft bounce.
• Use of confirmed opt in can help you to avoid inadvertently adding spam traps to your database.
• Don’t block the exit – provide contacts an easy way to unsubscribe and honor their request.
• Create a policy to address chronically disengaged contacts, and act on that policy on a regular and rolling basis.
• Do not continue to email contacts who don’t engage with your mail in a year or more – this risks deliverability problems that can include a blocklisting.

Authentication Best Practices and Benefits

• To demonstrate that your mail is reputable, authenticate using SPF, DKIM and DMARC.
• Understand all systems that send mail on behalf of your brand and monitor each system.

Looking for more information?

In depth guidance can be found within the Adobe Experience Platform Email Deliverability Best Practice Guide.