Tuesday, July 10, 2018

Email Deliverability Causes and Solutions

We work hard to protect, nurture and grow our email DBs. For many, its our most effective marketing channel. Yet, according to Return Path, 20% of our emails never make it to the Inbox. Why? Only a small percentage of email deliverability issues are the result of bounces. The rest are being driven by 2 significant factors:
  1. Increased protection by ISPs against malware attacks and other malicious activities.
  2. Growing complaints by email recipients about unwanted/irrelevant emails, causing ISPs to implement their own mitigation strategies and solutions.
Below is a comprehensive summary on the subject, both from my own learnings and from other experts.

What affects email deliverability?

ISPs (such as Gmail, Hotmail, or Yahoo) decide which emails land in the inbox and which are blocked or bulked, all based on your overall email sender reputation.
  • Blocked: The ISP takes action against poor IP reputation and refuses to accept your emails altogether. It doesn't get worse than this.
  • Bulked: The ISP accepts your email but routes the message to BULK or SPAM folders vs. Inbox. This is also determined by your overall sender reputation.

How is sender reputation measured?

Each ISP measures your IP/domain reputation separately based on several different metrics. Repeated issues with one or more of the red flags below will increase the chances that an ISP will block or bulk your messages.  
  •  Bounces
  • Complaints
  • Engagement
  • Authentication
  • Volume and Frequency
  • Blacklists and Spam Traps


There are two main types of bounces: soft bounces (temporary failures) and hard bounces (permanent failures).
  • Soft bounces technically have made it to the email server, however they did not reach the sender. This can happen because:
  • You’re sending to someone who’s mailbox is full
  • You’re sending to someone who’s account has been temporarily suspended
  • There’s been an error or outage at the receiving mail server
  • There is a problem with authenticating you as a sender, or you have a high degree of other reputation issues
  • BTW, an out-of-office reply is technically not a soft bounce, as it did make it to the inbox.
  • Hard bounces happen when the domain does not exist, is invalid, or the mailbox has become inactive. It is a permanent failure.
According to Oracle deliverability expert Pradeep Mangalapalli, bounce rates up to 3% for hard bounces and up to 5% for soft bounces are considered acceptable thresholds.


ISPs track every time a subscriber flags an email as spam. In some cases, ISPs share this information with email senders through feedback loops (a process by which certain email senders may be able to receive notification when recipients report emails as spam).
There’s a lot more to sender reputation than a spam complaint; however, a recipient marking an email as spam is the strongest negative signal to ISPs about an email. Spam complaint rates above 0.2% are considered high, and may result in poor deliverability. At ISPs, like Gmail, a spam rate as low as .08% can “start to affect” your deliverability.


ISPs track how subscribers engage with your emails through: opens, clicks, scrolling through a full email, deleting without opening and marking as read without opening. 


Spammers will spoof legitimate domains to send their emails, so it's important to adhere to all the latest security standards to protect your subscribers and your brand. ISPs will block messages that don't pass these authentication protocols:
  •  Sender Policy Framework (SPF): ISPs cross check the domain in your From address against the IP address listed in the public record in the Domain Name System (DNS). ISPs generally don’t block email solely because of a missing SPF record. However, it is one more data point that contributes to a sender’s reputation and it helps protect your brand.
  • Domain Keys Identified Mail (DKIM): Email senders generate public and private key pairs. ISPs lookup the public key in the public DNS record, and verify the matching private key in the email header. These days, messages not signed with a DKIM signature are very unlikely to see the inbox.
  • Domain-based Message Authentication, Reporting & Conformance (DMARC): The purpose of a DMARC record is to tell inbox providers WHAT you want them to do with email that doesn’t pass SPF and DKIM: allow it, filter it, or reject it. Soon, publishing a DMARC record will be necessary to ensure good deliverability to reputable inbox providers.

Volume and Frequency

When spammers spoof a domain, they take the opportunity to send extremely high volumes of email all at once. ISPs look at the history of your email volume and frequency. If there's a spike, this can affect your reputation. Sending higher volumes of emails is okay as long as you are consistent. ISPs are more concerned with past trends and spikes rather than overall volume.

Blacklists and Spam Traps

Spam traps are email addresses that either belong to an ISP or belong to an inactive user. Often ISPs will monitor email addresses that have been inactive for a long period of time, and convert these dormant email addresses to spam traps.
There are two main types of spam traps:
  • Pristine: Email addresses that are created and published online but never register for any marketing emails. If a spammer crawls web pages to harvest published email addresses, they may pick up a pristine spam trap.
  • Recycled: If a mailbox goes inactive for a long time, the ISP will convert it to a spam trap to identify senders that mail to inactive subscribers. It's not known for sure how long an email address remains inactive before it is converted, but anything over 12 months is generally suspect.
The net impact of a spam trap is that you get blacklisted. Landing on a blacklist can have various effects on your deliverability. In some cases its not a big deal, however getting on some blacklists, like SpamCop, can be severe and can take significant time to correct.

Email Setup

Emails that have HTML errors, such as image references or links that are dead can cause deliverability issues.

A Word About 'Sender Scores'

As you can see, deliverability issues are caused by many factors and can be difficult to accurately analyze. In the past, as spam decisions shifted towards sender reputation, the concept of an overall Sender Score emerged as a simple benchmark to help us quickly spot trouble. Because of increased complexity however, this simple sender score is no longer accurate or valid and should not be used as a KPI. As Kevin Senne, Sr. Director of Deliverability for Oracle states: “Senders were desperate for some kind of measure to explain email deliverability, and this number was something that they could look to as a guide”. Again, according to Mr. Senne, the problem is:
  • No major ISP uses the Sender Score metric to determine delivery or inbox placement.
  • The score doesn’t reflect the reality of deliverability success or failure.
  • It is mainly a US based system; the scoring does not accurately reflect performance for senders in EMEA, APAC, or Latin America.
 The best method of measuring deliverability currently is by monitoring the percentage of inbox placement across each ISP/domain separately, as well as monitoring open rates. For those that don't have access to Deliverability Tools, Oracle deliverability expert Pradeep Mangalapalli recommends using a unique open rate of around 10% as a general indicator of deliverability health. The best way to prevent deliverability issues is to follow the best practices below:

Best Practices to help mitigate deliverability issues:

  1. Avoid using third party lists to acquire new leads or grow your email database
  2. Obtain consent from contacts before sending them emails
  3. Regularly monitor bounce back rates and bounce back messages
  4. Regularly monitor and run reports to check spam complaints
  5. Review engagement metrics to help refine email programs
  6. Adhere to local and international email regulations
  7. Send targeted emails based on interests and contact preferences
  8. Regularly segment out inactive contacts (users who have not engaged with your emails in about 12 months). Repeatedly emailing recipients who aren’t engaging with your emails can be bad for your reputation for several reasons: 
  9. Addresses that don’t open or click on your messages are much more likely to mark messages as spam. 
  10. Unengaged addresses may have been repurposed into spam traps. 
  11. Unengaged recipients can make your traffic look unwanted by lowering your open rate percentages. 
  12. Stick to a consistent volume of email sends from month to month. 
  13. Consider email design best practices, such as using preheader text, alt text, and image-to-text ratios.

Other recommendations:

Manage Your Inactives. Suppressing all email records with no activity in the last 12 months is a scary thought for most of us, as it could greatly reduce our list size. There are email scrubbing services that will try and determine which specific email addresses have been converted to spam traps, honeypots, etc. so you don't have to suppress all inactives, just those that have been identified as harmful. Vendors include FreshAddress, Informatica and BriteVerify, among others.

Make it easy to unsubscribe. This sounds counter intuitive, but making the unsubscribe process as easy as possible is a really good idea. The truth is, if someone doesn’t want to receive your messages and they don’t see an easy way to unsubscribe, they always know where the “report spam” button is. Remember, someone who opts out can always opt back in, but even a small number of spam complaints can really hurt your reputation, not to mention your ongoing ability to deliver messages to those who want to receive them.

Be conscious of your sending frequency. If you feel like you’re doing all the right things with your email program, but you’re still landing in the spam folder, it may be a good idea to examine your sending frequency. Between your regular newsletter, special offers, and other announcements, you could be sending your recipients more email than you think. Exactly how much email is “too much” differs for every sender, but if your reputation is suffering, even moderately reducing the amount of email your recipients receive from you is a good idea and a great place to start.

Summary. Imagine if you were to gain access to 20% more of your DB! Those in charge of marketing automation platforms are making this possible by learning the causes, solutions and tools, as we become email deliverability experts.
Yet managing inbox placement is only half the battle. You still have to focus on level of engagement in order to keep your overall sender reputation in good health. A solid mix of good email data management, relevant content and continuous real-time deliverability monitoring is what currently works in keeping the inbox door wide open.

Steve Kellogg

Sources used for this post: Oracle Deliverability Plus, Litmus, Return Path



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