Troubleshooting Email Deliverability

Understanding email deliverability is critical to your email marketing success. Mailbox providers look at hundreds of signals to determine whether they should accept incoming emails, and whether to deliver those messages to the inbox or the spam folder. Your mailing patterns, data hygiene practices, user engagement, authentication, and content all play a part in how (and whether) your email is delivered.

If you're experiencing issues with open rates, click rates, spam complaints, or bounces, read this article to learn how to identify possible causes and find suggestions for resolving them.

# In this article

# Delivery vs deliverability

There are two categories of email delivery concerns: delivery and deliverability.

Issue Type	Problem	Metrics
Delivery	Messages are rejected.	Delivery rate is lower than usual, bounce rate is higher than usual. Delivery rates under 95% are generally considered low, however, rates above that may still have delivery problems.
Deliverability	Messages are delivered to the spam folder.	Deliverability is impossible to measure with precision. Mailbox providers don't provide data on how many emails they deliver to the inbox versus the spam folder. Open or click rates for a specific mailbox provider that are significantly lower than others may indicate a problem with deliverability.

# Identifying delivery and deliverability issues

Reviewing email performance metrics can help identify issues that might exist with email delivery or deliverability.

These topics describe delivery and deliverability metrics you can reference in Iterable and provide some examples for monitoring metrics over time.

# Iterable delivery metrics (bounces)

To get started, you need to know why your messages aren't being delivered. You can get this information by reviewing the bounce reasons in your reports.

# Bounces by category

To see bounces by category for a campaign, go to the analytics page for the campaign and click on Delivery. Find the Bounces widget and expand the reasons section.

To download all bounce events from this page, click Export Events, and select Email Bounce, then click Export. This provides a CSV file with a row for each email address that bounced, with bounce reasons in the recipientState column.

To learn more about bounce reasons and their meanings, read Email Bounce Event Properties.

# Bounce rates by domain

You can also run a segment analysis on the campaign and break down the results by domain. To do this:

1. Go to Messaging > Campaigns.

2. Find the campaign you're working on, and click View Analytics.

3. In the left hand menu, find Segment Analysis.

   • For Select a Segment, choose domain

   • For Select Metrics, choose email bounce rate

# Iterable deliverability metrics (open and click rates)

To troubleshoot deliverability, start by reviewing your metrics. In Messaging Insights, use the Segment Analysis view and break down the results for open rates and click rates by domain.

To do this:

1. Go to Messaging > Campaigns.

2. Find the campaign you're working on, and click View Analytics.

3. In the left hand menu, find Segment Analysis.

   • For Select a Segment, choose domain

   • For Select Metrics, choose email click rate, total email opens, and total emails delivered.

   • Note: email open rate isn't an available metric in the Segment analysis view. To determine your open rates, divide total emails opened by total emails delivered.

Review your results and look for trends:

• Low open rates for a majority of domains indicate that your audience isn't engaging with your content. When you see this, remove users who haven't opened or clicked on your emails for a long time and look at strategies to refresh your content.

• An open rate that is significantly lower for one domain compared to others could indicate that the mailbox provider is filtering your emails to spam.

In the example below, engagement is much lower at Hotmail.com, which strongly indicates that emails are being filtered to spam there:

Domain	Email open rate	Email click rate
Gmail.com	30%	1.2%
Yahoo.com	25%	0.8%
Hotmail.com	2%	0.01%
Comcast.net	27%	1%

# Monitoring metrics over time

It’s a good idea to monitor how email metrics trend over time for the most common mailbox providers on your list.

Observing how metrics trend over time can provide instrumental insights into your inbox placement performance and indicate when problems arise.

In this example, this trend in open rates shows a sudden drop at Hotmail, indicating a spam placement issue in June and July:

# Troubleshooting delivery problems (high bounce rates)

Problems with delivery happen when your messages aren't delivered to the contacts you're sending to because mail servers are rejecting your emails instead of delivering them. You know that you have a problem with email delivery when you see low delivery rates and high bounce rates.

To get started, find out who is rejecting your emails, and why.

• Who is rejecting your emails?

  To check which mailbox providers are rejecting your emails, you can view and download bounce events. For instructions, read Delivery Metrics in Iterable, (above).

• Why are your emails rejected?

  There are many reasons why mailbox providers can decide to reject your emails. In Iterable, a hard bounce means that the email address was rejected as an invalid user, and a soft bounce is any other error.

  To view possible reason codes for bounce events in Iterable, read Email Bounce Event Properties.

Common reasons that emails bounce include:

• Poor list hygiene and bad email data.

• Increasing your send volume too quickly, like when warming a new IP or domain.

• Reputation problems with your domain or IP address.

• Being blocklisted.

• Authentication errors, such as problems with your DNS records.

• Content problems.

# Troubleshooting deliverability problems (spam folder placement)

Email deliverability has to do with inbox placement. Mailbox providers’ spam filtering algorithms analyze hundreds of elements to decide if your emails should be delivered to the inbox or the spam folder. You have a problem with deliverability when mailbox providers place your emails in the spam folder.

Deliverability is impossible to precisely measure because mailbox providers don't provide data on how many emails they deliver to the inbox versus the spam folder. When you see open and click rates that are significantly lower for a specific mailbox provider compared to most others, this indicates trouble with email deliverability.

Why are your emails going to spam?

Among the most common causes for spam placement:

• Negative user engagement, such as spam complaints and lack of engagement.

• Warming up a new IP or domain or other sudden increases to your mail volume.

• Email content problems in your HTML code.

# Gmail placement: the Promotions tab is the inbox

Marketers may feel concerned to discover that their emails are placed into the Gmail Promotions tab instead of the Primary tab of a Gmail inbox. Marketing emails are meant to land into the Promotions tab in Gmail.

Some things to know about Gmail tabs:

• The Promotions tab is the inbox. The alternative would be the spam folder.

• Most users don’t have tabs. Tabs only show up in the Gmail website or Gmail app. Users reading their emails in Apple Mail or iPhone mail apps don't have Gmail tabs—messages are either delivered to the inbox or to spam.

• Some email marketing authorities report higher conversion rates when emails land in the Promotions tab, probably because users expect marketing content and are in the mindset of making a purchase. (Because the Promotions tab sets user expectations, another benefit is fewer spam complaints and unsubscribes.)

• Don't try to game the system. Google uses smart filtering and machine learning, and you won't be able to use tricks to change your inbox placement.

• Gmail categorization is different for each user. The same message may be delivered to the Promotions tab for one user, and to the Updates tab for another. Multiple factors that influence inbox placement and tab classification, including user engagement, your sender address, and whether an email contains mixed content (both marketing and transactional).

This is how Gmail describes the purpose of each category:

• Primary: Emails from people you know (and messages that don’t appear in
  other tabs)

• Social: Messages from social networks and media-sharing sites

• Promotions: Deals, offers, newsletters and other “call to action” emails

• Updates: Notifications, confirmations, receipts, bills and statements

• Forums: Messages from online groups, discussion boards and mailing lists

To avoid having your transactional emails land in the Promotions tab:

• Use separate subdomains and/or IPs to distinguish transactional from marketing campaigns.
• Ensure that there is no promotional content whatsoever in your transactional emails.

To learn more about Gmail tab sorting, read Making Gmail’s tabbed inbox work better for you (Google).

# Recommended actions

To improve your email delivery and deliverability, here are Iterable's recommended actions to address the various causes.

# Improving your data hygiene

A high number of HardBounce, SoftBounceMailboxFull, Suppressed, and SoftBounceDnsFailure bounce reasons indicate that your list contains invalid or inactive email addresses.

Possible causes for bad list data include:

• List acquisition problems

  • List data and emails sourced from unsecured or poorly designed web forms can include problems ranging from typographical errors (typos) to malicious bot activity. Signs of bot activity include:

    • Bounces coming from unusual domains might be users created by a bot.

    • Bounces where the username portion of the email address (username of username@example.com) follow a similar pattern (like bob123, mark123, and daniel123) might be users created by a bot.

  • Sending to purchased lists or email append services.

• Segmentation problems

  • Did you email an old list by mistake?

  • Did you forget to add a suppression list?

  • Did you recently start using a new data source that may contain invalid email addresses?

To address high bounce rates caused by bad data, clean up your email lists.

• Do not purchase lists or email append services. Purchasing lists or sending to users who have not opted in to receive your emails may violate US CAN-SPAM laws and is against Iterable's Anti-Spam Policy. Iterable disables accounts that violate this policy.

• Remove users who bounce again and again. For example, you can create a journey to remove users who continually bounce for reason SoftBounceMailboxFull. For instructions, read Unsubscribing Bounced Users.

• Use a list validation tool to clean your lists before importing them to Iterable. To learn more about one tool that can do this, read Kickbox + Iterable Integration.

• Secure your web forms. Use a reCAPTCHA or honeypot mechanism on your web forms to prevent bot sign-ups and other kinds of abuse.

To learn Iterable's recommendations for good data hygiene, read Maximizing Email Deliverability.

# Slowly increasing your daily email volume

Mailbox providers don’t like sudden spikes in daily volume and changes in mailing patterns. A large increase in volume, either during a warm-up period, or when sending a high-volume campaign from an existing sender, can cause problems with both delivery and deliverability.

These problems include:

• Bouncing — If you warm up too fast, or suddenly and significantly increase your daily volume, your sender may have been blocked. This causes your messages to bounce. These types of blocks tend to be temporary. Wait a few days and check if you are still seeing issues.

• Poor inbox placement — Spam placement issues are also common during warm-up. Mailbox providers can take about a month of regular sending to assess your emails before deciding if you are worthy of the inbox or not.

The next time you plan to send a large volume of emails, stagger the send across multiple days to avoid rejections.

If you are warming up a new domain or new IPs, slow down. The best practice is to increase daily volume in increments of up to 25%.

To learn more about warming up a new IP address for sending email, read our IP Warm Up Guide.

# Addressing negative user engagement

The way users have engaged with your emails in the past plays a very important role in your deliverability.

• Opens, clicks, forwards, replies have a positive effect on your reputation, as they indicate that users are engaging with your emails.

• Spam complaints and emails deleted without being read, on the contrary, show that users don't want to read your emails.

Try to understand why users are complaining. Begin by identifying the campaigns generating higher complaint rates, and consider the following:

• Are you managing expectations well when a user registers, in regards to the type of content you will send and how often they will receive emails from you?

  • Are you sending too often?

  • Are you sending the type of content that the users are expecting?

• Is your content engaging enough?

• Is the unsubscribe link visible? Does it work? Is it an easy process to unsubscribe? An unsubscribe link that is hard to find can cause spam complaints.

To address negative user engagement, you can:

• Suppress users who have not clicked or opened any email in a long time. Stop sending to users who aren't engaged; this hurts your inbox placement.

• Apply stricter engagement suppressions to the domains that filter your emails to spam. For example, if your emails have been landing in spam at gmail.com, consider restricting your segment of Gmail users to include only users with email clicks or email open events in the past 90 days. Do this until you start seeing improvement.

• Try to re-engage users before letting them go. For advice on how to set up a re-engagement campaign or journey, contact your Iterable customer success manager.

# Addressing domain or IP reputation problems

Mailbox providers reject emails that they identify as unwanted. This happens, for example, when too many of their users have reported your emails as spam.

Use Iterable reports to identify which campaigns generate high spam complaints, and take action to address the root cause. This might include actions such as:

• Managing users' expectations by disclosing of the type of content you send and how often you send those messages.

• Adjusting your segmentation to ensure an engaged audience who cares about your content.

To send to a mailbox provider that is rejecting you, restrict your user segments to new and recently engaged users. This rebuilds a positive reputation over time (usually a few weeks).

If these actions don't resolve your issue, contact technical support.

# Addressing blocklists

Most email providers use spam filter services that maintain a list of IPs and domains that are known for distributing spam. There are hundreds of blocklists around (sometimes called "blacklists"). Usually, senders get listed when they have hit spam traps or generated too many user complaints.

There are hundreds of blocklists around, but only a few of them have a significant impact on delivery (Spamhaus, Spamcop, URIBL, SURBL, Barracuda). If your sending IP, sending domain, or any other domain in your email content are listed on any of these lists, your emails might be filtered to spam or rejected.

To know if this is the case, you can use a resource like MX Toolbox or another blocklist checker.

When searching a blocklist, look for the presence of the following:

• Your sending IP(s)
• Your sending domain
• Any other domain in the email content (such as links, images, reply-to addresses, etc.)

You should also directly check some filter-specific blocklists and request removal if necessary. These include:

• Barracuda
• Proofpoint (Apple Mail)
• Office 365

Address the root cause before you request to be removed from the list. Otherwise, you may be listed again for the same reason — and the blocklist owner may refuse to de-list you for repeating unwanted behaviors.

# Addressing authentication problems

Typically, SPF and DKIM authentication are set up for Iterable projects during implementation. However, changes made to your domain's DNS records may result in failures.

Send yourself a proof of the campaign to a Gmail account and look at the email header. Can you see if SPF, DKIM, and DMARC pass?

To learn how to check, read Trace an Email with its Full Headers (Google).

If authentication fails, you can contact technical support.

# Addressing email content problems

Sometimes, it can be something within the content of an email that triggers spam filters and causes spam placement or bouncing. Carefully review your content and make sure you follow best practices.

• Identify the offending content. Run some tests until you are able to identify which part of the content is causing the issue. For example:

  • Start by testing a plain text version with no links.

  • Then add HTML content, block by block, until you find which part of the email contains the problematic content.

• Check if any of the domains in your content are on a blocklist. You can use MX Toolbox or another blocklist checker. To learn more about blocklists, read Addressing Blocklists above.

  Every domain carries some level of reputation, not just your sending domain. This includes links, short links, images, and any other elements of the message that contain a URL or domain.

  For example, if you use a platform for image hosting and their domain has a bad reputation, this could negatively impact your deliverability and land a message in the spam folder.

• Avoid third-party URL shorteners. Shortening services are often used by spammers to mask destination URLs and are considered an element of suspicious content.

• Make sure your HTML content is suitable to send. Check that your email's HTML complies with W3C web standards and is free of errors. To do this, use an HTML validator (FreeFormatter.com).

To learn more best practices, read Maximizing Email Deliverability.

# Additional resources

# Third-party metrics for certain domains (Gmail, Microsoft)

Some ISPs provide bulk email senders with reports on their domain's sending performance within their networks. These reports contain additional insights for delivery and deliverability with users of their respective domain(s). To access to these reports, set up an account with:

• Gmail — Use Google Postmaster Tools to monitor users with the email domain gmail.com.

• Microsoft — Use Microsoft SNDS to monitor users with the email domains outlook.com, hotmail.com, msn.com, and live.com. If you have a dedicated IP, ask your Iterable customer success manager for help setting this up.

# Third-party deliverability tools

Because deliverability can't be directly measured, there are some services that specialize in inbox placement insights, such as our partner, Everest (by Validity).

Usually, these services provide a seed list of several hundred emails, representing many mailbox providers. Next, attach that seed list to your campaigns. Once you start sending to the seed list, you can view reports on how each seed received your email: did it reach the inbox, go to spam, or bounce?

These tools can be useful to identify trends, however, user engagement plays an important role in spam filtering, and these seeds don't engage with your emails (they don't open or click messages). Because seeds don't behave like real users, this can sometimes lead to false positive data.

# Still need help?

To learn about Iterable deliverability services, including monitoring and support, contact your customer success manager.

# Want to learn more?

For more information about some of the topics in this article, check out these resources. Iterable Academy is open to everyone — you don't need to be an Iterable customer!

Iterable Academy

• Deliverability Troubleshooting
• Deliverability Scenario: Oopsies!

Support docs

• Maximizing Email Deliverability
• Messaging Insights
• Email Bounces
• IP Warm Up Guide
• Monitoring Gmail Deliverability with Google Postmaster Tools
• Gmail Promotions Tab Annotations