Fact or Fiction? Deliverability Myths Debunked

Just like Bigfoot or the Loch Ness Monster, deliverability myths have long been a topic of debate. While getting to the inbox is like the mythical “white whale” for a lot of businesses, it doesn’t have to be.

By debunking some of the following myths, understanding deliverability and how to better reach the inbox should no longer be a mystery.

Fact or Fiction? If I have insight into my engagement metrics, that should tell me what I need to know about my inbox placement.

Fiction! Although engagement metrics such as clicks, read rate, and opens are great, they don’t always directly correlate to your inbox placement. The bottom line is that different metrics measure different aspects of your email program. Engagement metrics do exactly what they sound like they do; they look at how your customers are engaging with your mail—not whether they received it. Deliverability metrics look at where your mail gets delivered (inbox, spam, or missing) and act as a basis for your engagement metrics. Not only are engagement rates a poor measure of deliverability, you’ll also get an inaccurate picture of engagement if you don’t understand your deliverability.

Fact or Fiction? Complaints can come from places other than just the “This is Spam” button.

Fact! Your complaint rate largely consists of customers reporting mail as spam, but it also includes other metrics such as:

  • A customer reaching out directly to the mailbox provider and complaining about the mail
  • A customer sending a complaint directly to a filtering application or a complaint-driven blacklist
  • A Microsoft SRD (Sender Reputation Data) negative vote: Microsoft uses their own method to track unwanted mail called Sender Reputation Data. To collect this data, Microsoft reaches out to their customers and asks whether they wished to receive certain pieces of mail. If the customer says no, it is called a junk vote and is counted as a complaint.

Fact or Fiction? Having a list unsubscribe link in the footer of my email is sufficient.

Fiction! CAN-SPAM legally requires you to include an easily viewable unsubscribe link in all of your email messages. But that alone is often not enough to mitigate customer complaints. Adding a list-unsubscribe header is a great way to improve your deliverability by reducing complaints. Gmail and Outlook in particular are adopters of this method and recommend adding the header as a best practice. The list-unsubscribe header is a simple concept that shows the unsubscribe link in the email header so that customers don’t have to dig for the unsubscribe link in the footer of the email. Plus adding the list-unsubscribe header helps customers avoid getting blacklisted on Lashback and SORBS.


Fact or Fiction? If I am missing 100% consistently at a mailbox provider then I must be blocked from that mailbox.

Fiction! A 100% missing rate is sometimes an indicator of a block, but that is not always the case. Consistent 100% missing rate could indicate:

  • A seeding issue, which could be across multiple mailbox providers or just one. To determine whether you have a seeding issue, make sure this occurs consistently across campaigns and seeds. Often, Inbox Optimizer (part of Return Path’s Inbox Monitor tool) will call out “seeding” in the issues column. Also check, the “seeds to suppress” tab in Inbox Monitor at least quarterly, to make sure you are suppressing the right seeds—otherwise they will show up as missing.


  • Check for a Cloudmark fingerprints. If a sender is prone to high complaints and spikes in spam traps, check to see whether Cloudmark fingerprints might be culprit.
  • Check your IP address reputation. Some mailbox provider postmaster sites offer a tab to check the reputation of an IP address. For example, AOL allows you to check the reputation of any IP address. The reputation of the IP address determines whether or not the sender has a good enough reputation, and a poor eputation could result in 100% missing.
  • Last but not least, check your SMTP bounce logs if possible. Bounce logs often have great insight into what issues you might be experiencing. By going to the postmaster site of the given mailbox provider and searching for SMTP error codes, you can often figure out why your messages are continuously bouncing.  Often the SMTP bounce logs will even indicate a block if that is in fact the issue.

Fact or Fiction? Certification can improve my deliverability.

Fact! Return Path’s Certification program provides qualified senders an opportunity to be “whitelisted” with with major mailbox providers like Yahoo, Microsoft, AOL and more. Once certified, mailbox providers acknowledge you as a safe sender, so in turn, your emails receive reduced filtering at participating mailbox providers. By following the standards of the Certification program and staying below the thresholds, you receive the benefits of Certification hat your competitors might not have.

Although Return Path Certification cannot guarantee inbox placement, it is likely that certified senders will see improved inbox placement. Return Path’s global coverage is the widest in the industry covering AOL, Yahoo!, Microsoft, Cox, Comcast, Yandex, Cloudmark, Mail.ru, Orange, Spamassassin, and Spam Cop. Certification has other perks that help with inbox placement, such as unblocked images and active links, bypassing mailbox filters, real time alerts, and professional assistance.

To learn more about Certification, please visit the Certification page on our website, then apply here.


To learn more about deliverability, check out our latest ebook, The Ultimate Guide to Email Deliverability.

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