Deliverability Basics

Written by Orlando Kalossakas

More than 20% of legitimate emails don’t make it to the inbox.

In order to ensure your emails are properly delivered, a number of requirements must be satisfied. Here, I sum up some key points to keep in mind when considering the importance of deliverability.

Reputation Monitoring

Sending campaigns requires you to watch and protect the your sender reputation. Your reputation is dictated by a few things:

• The reputation of any URLs used in your campaigns
• The domains and IP addresses used for sending
• Where your images are stored (CDN, different domain, etc.)
• The content of your message

It's important to monitor all of these factors to ensure that your sender reputation remains clean. Make sure you send from a clean IP and that any content you link out to or pull into your email is served via a safe domain. Additionally, it's a good idea to regularly run spam testing on your emails. Seeing how tools like SpamAssassin grade your emails is a good first step in identifying any possible issues you may run in to.

SPF, DKIM & Domain Keys

When it comes to verifying senders, there are three main tools at the disposal of ESPs, email clients, and ISPs:

• Sender Policy Framework (SPF)
• Domain Keys Identified Mail (DKIM)
• Domain Keys

The objective of these systems is to guarantee and verify the identity of the senders and protect the receivers from insecure emails. Typically, these tools have the biggest impact on fighting phishing emails, which often originate from odd-looking domains attempting to impersonate legitimate companies.

Properly implementing all three is vital to keeping your deliverability rates high. Many ISPs and email providers consider non-authenticated emails suspect and send them to the spam folder. Fortunately, many email service providers make setting these up quick and easy.

Send Throttling

ISPs react differently to receiving large quantities of emails from a single source. Some may impose temporary or permanent volume restrictions. Others won't blink an eye.

To cover both cases, most ESPs can slow down, or throttle, the sending of a campaign. Throttling large campaigns helps to distinguish legitimate mail from typical spammy "batch and blast" sends. Throttling can be an excellent way to ensure that your messages are delivered safely to a subscriber's inbox. and help to maintain your sender reputation, since fewer bounces are likely to occur.

HTML Optimization

Making sure the actual markup of your emails is well-formed is a great way to help ensure deliverability. Many spam filters and email providers will grade poorly-formed HTML as potential spam. When their parsing engines have trouble "reading" the HTML, there's a good chance that it could be sent from a malicious spammer or someone who doesn't know what they are doing.

Most email designers don't worry too much about actually validating their code, but at the bare minimum, you need to make sure the code in your email doesn't contain any missing or open tags, or any weird markup that could set off alarms.

Feedback Loops & ISPs

Sending an email out to a group of people is kind of like sending a satellite into space: once in orbit, you need to make sure you are receiving feedback from the satellite and making adjustments as necessary.

Having a feedback loop in place is an extremely important part of monitoring your sender reputation. As a basic first step, you need to monitor any replies to your email campaigns. Whether it's a complaint, positive feedback, or someone that doesn't understand an unsubscribe link emailing to be taken off a list, your reputation could suffer if you don't honor these complaints and requests.

Having a feedback loop with ISPs is another step in mainting your reputation. Understanding when and why people click on "report as spam" buttons, monitoring hard and soft bounces, and unsubscribes is necessary for a good email program. Maintaining high-quality lists is, too. Regularly cleansing your lists helps prevent disengaged subscribers from blacklisting your messages and forcing ISPs to block messages for your other subscribers.

Deliverability Tips

Here are some actionable takeaways to help with your deliverability. While many of these things are handled by an ESP or IT department, understanding them is a necessary pillar in the foundations of understanding email marketing.

• Make sure your sending address and servers are properly configured.
• For automated messages, you may want to set up a separate sending address e.g. "notifications​@yourdomain.com" or "billing​@yourdomain.com".
• Likewise, if you're sending an email that someone could potentially respond to (like support notifications), use an address that is monitored by someone at your company and that all emails to that address are addressed in a timely fashion.
• Make sure your HTML is, if not completely valid, well-formed. Check for missing tags, typos, and weird markup to ensure that spam filters don't unnecessarily mark your messages as suspicious.
• Prioritize and manage the flow of email that you're sending. If you send a ton of email, try throttling it to reduce bounces and blocking.
• Always keep your eyes on the data. Monitor your analytics and use that data to gather insights not only into your deliverability, but the content of your emails based on open rates, click rates, and engagement.

My name is Orlando and I work at Mailjet, a company specializing in sending, tracking, and delivering marketing and transactional emails. Check what we do to enhance deliverability at www.mailjet.com.

Further Reading

Word to the Wise Blog
Deliverability.com Blog
Gmail Bulk Senders Guidelines
The Ultimate Guide: How to Prevent Emails from Landing into the Spam Folder
How to Avoid Spam Filters
Return Path Guides
Your Reputations Holds the Key to Deliverability
Key Facts on Email Deliverability You Want to Know
Improving Deliverability
10 Ways to Suck at Email Deliverability