Email Deliverability Troubleshooting

Table of Contents:


Deliverability Best Practices a Short Summary

  • To better ensure that your messages are delivered to the inbox, it is recommended to follow sending best practices, by only sending to directly opted-in subscribers that are actively engaged with your email streams. Moreover you should periodically deactivate subscribers (proactively set their status to unsubscribe or exclude them from all normal campaigns), that no longer engage with your email streams.
  • A good rule of thumb is that actively engaged subscribers will open and/or click on your daily messages at least once in a 30 day time-frame and at least once on your weekly messages within 30 days.
  • Any subscriber that has not opened or clicked on your messages in the past 12 months should be permanently deactivated (set their status to unsubscribe), as they run the risk of turning into a spam trap. Alternatively you can remove them from your list altogether if you don't need their behavioral history, but in that case you should consider adding add them to either a Global or List Level suppression list.
  • You should also make sure that your signup page or forms have anti-abuse measures in place such as captcha or email verification. A good way to avoid typo’s is simply require them to type the email address twice into your form. All this in order to avoid having high rates of hard bounces, complaints and low delivery and read rates, all of which cause poor reputation and delivery, and high spam foldering.
  • Also see our Apple MPP knowledge base doc, where you can find lots of information on how to target engaged users in a world where open engagement stats are less reliable.

For SMS Deliverability Best Practices, you can refer to our online documentation of SMS Campaigns, and see there SMS Deliverability Best Practices.

Deliverability and Sending Reputation Getting Started

Sending IP

(info) In order for your email messages to reach the inbox of your users, you must have a good Sending IP and sending Domain reputation.

Sender reputation is a score that an Internet Service Provider (ISP) such as Gmail, Outlook, etc. assign to an organization identified by their IP and sending domain. The higher the score, then ISPs will more likely deliver emails to the inboxes of recipients on their network. On the other hand if the score falls under a specific limit, the ISP may send email messages to recipients’ spam folders, or even reject those messages altogether which will result in soft bounces.

(info) The reputation is based on how recipients interact with the email messages coming from that organization's sending IP and sending domain. For example, the more recipients, open, click, and reply to those messages, the higher reputation that Sending IP and Domain will have. And the opposite, the more recipients, delete without opening, or if there are high rates of unsubscribing, or marking as junk, will reduce the organizations' Sending IP and Domain reputation.  

Sending Domains

Make sure you have your domains authenticated as per the ESP guidelines. The two main authentications that allow you to establish your identity with ISPs are the Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) protocols. It is mandatory to have these authentication protocols in place. Visit our Email Authentication Protocols page, for more about the Authentication Protocols.

Assign List Specific Sending Domain/s

When you are setting up a new Sending List; make sure to have a domain that does not crosswire with other domains in other sending lists. It is best to use List specific ESP connections by locking ESP connections to Sending List. You can restrict one or more SMTP vendor connections to a specific sending list. Visit our List Manager page and see How to allocate and restrict one or more SMTP vendor connections to a specific sending list.

Align Sending Domains,Tracking Domains and Image Domains

(info) It is best practice to have the Sending domain, Tracking domain, Image domain and Bounce domain, all share the same top level domain.

So for example, if your sending domain is “” then make sure to have a tracking and image domain that share the same, so they can be "" and "" (or "" or ""). In case you are using vendors that require the Bounce domain to be setup in Ongage, then make sure to that the Bounce domain shares the same top level domain as well e.g., “”.

Test Mail

It is advisable to check your Mail Tester score when you start sending email messages and then do it periodically to identify if there are any issues with your IP reputation. Visit our Campaigns page and see How to Send a Test Campaign and use a Mail Tester.

List Hygiene

It is highly recommended to use a List hygiene mechanism for all channels from which email data is going to be added into your lists. These mechanisms include:

IP & Domain Warm Up

Deliverability Performance Monitoring

Ongage Reports

Aggregate Report

By using Aggregate Reports, you can see the complete email delivery status as sent, success, failed, hard bounces, soft bounces per campaign. By using this report you can check the status of soft bounces by applying additional filters like Per Day, Per Week, Per Month etc., to see if the number of soft bounces is increasing or decreasing. Visit our Analytics page and see the Additional Analytical Groupings.

Per Day Report

The Aggregate Report displays the statistics according to per day, which is an easy way to see daily trends particularly in Soft Bounces, Unique Clicks, Unique Opens and CTRs. And thus identify any trending issues. 

Per Week and Per Month Report

The Per Week and Per Month Reports are a great way at looking at trends across a wider span of time, and thus identify more consistent and long term trends.

Matrix Report

The Matrix Report enables viewing and analyzing deliverability (sent, success, fails, soft bounces, etc.) and performance statistics (opens, clicks, unsubscribes, etc.) grouped by the ISP domains. It gives you important insights about your sending domain reputation associated with the sending vendor connections used to send to those ISP mailbox domains. In the matrix report you can find the top ISPs you are sending to. Among those top ISPs, you can identify if there are any issues for that particular ISP. If you notice there are issues with Other domains, you need to check the full long tail report by using the Custom Aggregate Report (see below). Visit our Analytics page for more about the Matrix Report.

Custom Aggregate Report

The Custom Aggregate Report provides a way to view full long-tail report of delivery stats to all ISP/Mailbox domains that you are sending to. The Custom Aggregate Report enables additional custom groupings including the Grouped by Top Level Domains. Visit our Analytics page and see there the Custom Aggregate Report.

Deliverability Reputation Monitoring Tools

Built-in Mail Tester

Ongage has a built-in mail tester available using which you can send a Test Campaign from Ongage UI and generate a detailed Mail Tester report. Visit our Campaigns page and see How to Use a Mail Tester.

3rd Party Deliverability Testing and Monitoring Tools

Google Postmaster

This email deliverability tool is used to track data on a large volume of emails that are being sent and find data about your sending domain. Google Postmaster is a great tool in order to monitor your sending domain reputation in Gmail. To know more about Google Postmaster, visit here.

Microsoft Smart Network Data Services (SNDS)

This is the Outlook equivalent of Google Postmaster

Verizon Media Postmaster Tools

This is the equivalent of Google Postmaster for AOL, Verizon and Yahoo!

Other tools include:

Deliverability Issues and Relevant Action Items

High Hard Bounce Rate

Configure Double Opt-in

Double opt-in is the feature where email addresses are verified by sending an email asking to confirm the subscription. Double opt-in is the way to ensure that your email list is populated with accurate addresses from individuals who have consented to receive messages from you. Double opt-in is not a mandatory practice, but we recommend it to ensure the quality of your list. This feature helps you in maximize engagement rates, and keeps negative signals at check, which helps in building high sender reputation which means you'll have great email deliverability.

In this method you first obtain the subscriber’s email address through a contact or sign-up form. Then you send an email to the address they provided, asking them to confirm their interest and consent. See our List Settings help doc on how to implement Double Opt-in in Ongage.

Configure a List Validation Service

List Validation is the process where you can clean your email address lists to ensure you have removed all the invalid, high-risk, low score and even spam-trap emails addresses. Validation services typically employ an array of network data, Internet data and AI technologies in order to determine these factors.

Email List Validation aka Cleaning and Hygiene

  • Cleaning an email list is a process that checks whether the list of email addresses is valid/deliverable or not.
  • In email marketing, maintaining a clean list is a crucial task to ensure sender reputation and maximum deliverability by reducing hard bounce rates.
  • A list cleaning service will remove all hard bounces as well as a certain percent of dubious email addresses (such as spam traps).

Following is a list of some of the major email list validation services. We recommend speaking to an Ongage Account Manager for advice and introductions to anyone of the services below.

Double Opt-in

Using this method, you first obtain the subscriber’s email address through contact or sign up form. Then you send an email to the address they provided, asking them to confirm their interest and consent. Double opt-in is not a mandatory practice, but we do recommend it to ensure the quality of your list. The Double Opt-in feature helps you in building relationships, maximizing engagement rates and keeping negative signals at check which also helps in building high sender reputation which means you have excellent email deliverability.

Do not buy lists from 3rd party sources

(warning) We strongly advise not to buy lists from third party sources. There are a number of reasons that will affect your email deliverability when using purchased third party sources. A few of the reasons include:

  • Email addresses may be incomplete causing high hard-bounce rates.
  • There may be email addresses which no longer exist anymore, that too will create high hard-bounce rates.
  • There are chances that other people might be using the same list which can cause high complaint rates.
  • Such lists may even contain spam-traps which are extremely detrimental to sending reputation.

High Soft Bounces

(info) An increase in the number and rate of Soft Bounces is one of the strongest indicators of poor sender reputation.

There are other reasons for soft bounces and those include:

  • Email delivery fails due to a temporary issue like a full mailbox, or an unavailable server.
  • The email was too large (rare).
  • Email messages appeared suspicious or did not meet the receiving servers standards (due to possible usage of spam like content and/or content not accepted by the ISP). 
  • Your sending domain is not authenticated.
  • Your IP/Domain was not properly warmed-up.
  • But as noted: most significantly higher and increasing soft bounce rates will happen when one has poor Sending IP and/or Sending Domain reputation, with some/most/all of the ISPs you're sending to.

Identify Reason

  • One of your most powerful tools for understanding the nature of your soft bounces is with the Ongage Contact Activity Report.
  • Visit our online Analytics help documentation and see there: Contact Activity → How to View Bounce Reasons in the Contact Activity Report

Additional deliverability tools to identify the reasons behind your soft bounces are:

  • Mail Tester to check whether your sending IP is blacklisted or blacklisted. If your sending IP is blacklisted in any of the major blacklists, then the Mail Tester report will show you a negative score and highlight the blacklist in which the IP is listed.
  • Use the Ongage Matrix report to identify which ISPs you're getting blocked in (i.e., high SB rates). 
  • Use Google Postmaster tools to check your IP and Domain Reputation.
  • For Outlook (,, and use Microsoft Smart Network Data Services (SNDS).
  • For AOL, Verizon, Yahoo! use the Verizon Media Postmaster Tools.

Action Items

  1. Use a Cool down soft bounce exclude segment. Visit our Segments online help page and see How to Cool Down and Automatically Exclude Soft Bounces.
  2. Re-Warm Up your Sending IP and Sending Domain
    1. There are two options either you can do a General Warm Up plan, or an ISP specific Warm Up, e.g., only emails ending with
    2. The General Warm-Up is the easiest, but if you only have an issue with one ISP (mailbox provider), you may not want to scale back all your sendings. 
    3. The primary goal is to reestablish a positive sending reputation with mailbox providers.
    4. When re-warming up, in order to re-establish your sending reputation, you should warm-up with your most engaged contacts, e.g., recent clickers in the past 30 days.
    5. See our online documentation about: Automatic IP & Domain Warmup and/or  Manual IP & Domain Warm Up and use those plans to warm-up using your most engaged contacts.

Low Open Rates

Typically increasing higher soft bounce are going to go hand in hand with lower open and click rates. If your soft bounce rates are fine and still you have low open rates then this would be the measure. The other factors responsible for low open rates are:

  1. Sending emails to non active contacts.
  2. Sending too many email messages.
  3. Email messages are landing in the spam folder.
  4. Using an unsegmented list for sending your email messages.
  5. Sending your subscribers irrelevant content.

In order to improve your open rates follow the action items below.

Action Items

Auto Exclude Non Openers from your Campaign

Use the Auto Exclude the non-openers and send the email messages only to the engaged contacts. The Auto Sunset is a process of excluding non-active users from your mailing list. This can be achieved in Ongage by creating a default exclude segment which includes contacts in your list who have Not-Opened your campaigns in the last X days.

X is typically 15-90 days depending on a variety of factors (like how often you mail a contact). To know more about Auto Sunset, visit our Segments page and see there How to Auto Sunset Contacts using The Default Exclude Option.

Deliverability Testing Tools

Use Deliverability testing tools such as above to check which ISPs have low inbox placement rate.

Other Checkpoints
  • Your authentication protocols must be in place which will protect your messages from landing into the spam folder.

  • You are targeting the appropriate audience for your messages.

  • One of the important factors that affects open rates is if there are High Soft Bounces and High Hard Bounces.

  • Sending Volume: Initially start sending emails in low volume. Gradually increase the number of contacts over a period of time.

  • Maintain your sending schedule and frequency.

  • Buying and using lists from third party sources.

  • Maintaining your list and excluding all the inactive contacts.

High Unsubscribe Rates

(info) Note: increased unsubscribe rates is not a delivery issue (in fact, it's a sign of good deliverability, as unsubscribes is typically only done by users after the emails have reached their inbox!). By and large it is a targeting issue. Factors for increased unsubscribe rates can be:

  1. Contacts weren't clear they were signing up for emails.
  2. It could be a sign of email fatigue, and the need to offer contacts frequency options for getting less messages.
  3. Could be natural attrition, where a group of older less engaged contacts no longer want to get emails. The previous point, is the best way of managing and mitigating that.

Action Items

Following are some action items to perform to try and understand the cause of increased unsubscribes: 

  1. Check your lead collection forms, are they completely clear to contacts that they'll be receiving email messages upon submitting their email address.
  2. Check the Aggregate report for a period of at least 6 weeks to see if the phenomena is cyclical, e.g., more unsubscribes on weekends or certain days of the week.

  3. Run the aggregate report using the default campaign grouping and try and identify any set of campaign(s) that triggered higher than usual Unsubscribes.

  4. Create a segment of unsubscribes for those days where you seen a notable increase, and run a contact search on it to see if there's any correlation between their Create Date and Unsubscribe Date.

    1. You can run a Contact Activity on that Segment and select 4-6 weeks time-frame leading up to their unsubscribe, and try and learn about your sending frequency to them, and their open and click history leading up to the unsubscribe.

Additional Tools

Other Spam Testers

You can use these tools to analyze your current email sending reputation. These tools will show you what is impacting your score, and reputation, and provide info on what is missing or needed, in order to improve it, for better inbox placement.

  1. Mail Tester: Online documentation about mail tester.
  2. IsNotSpam:
  3. Postmark Spam Checker:

Spam Filters

There are a variety of common Spam filters that are used to examine the spam score of an email, and thus determine if an email will be directed to the inbox or spam/junk folder, or even rejected altogether. In addition, ISPs like Gmail have their own proprietary algorithms they use to determine this.

About Razor

Vipul's Razor is a checksum-based, distributed, collaborative, spam-detection-and-filtering network. Through user contribution, Razor establishes a distributed and constantly updating catalog of spam in propagation that is consulted by email clients to filter out known spam. Detection is done with statistical and randomized signatures that efficiently spot mutating spam content.

Important to Know about Razor:

  • In addition to the above, Razor also bases its scoring on the reputation of your sending domains as well links in your email and tracking domains.
  • If you're being flagged by Razor, you'll want to check those domains on Blacklist tools like those noted above – starting with the first one indicated there mxtoolbox.
  • Last but not least, you should check your email message content, and make sure it is not using spam like words or other content elements that might get marked as spam. If you're using any such content elements, then make sure to change and update your content to something less spam like.

Spam Cannibal

SpamCannibal uses a continually updated database containing the IP addresses of spam or DoS servers and blocks their ability to connect using a TCP/IP tarpit.

Blacklist Resources

The following web tools can assist you in determining whether the domains you're using in your emails are listed in any Blacklist. Simply enter your domain in one of the provided tools and examine the results:


  3. (recommended to run the test twice). Recommended to check this one out. In drop-down there you want option 1. 

  6. Cisco Talos Ip & Domain Reputation Center.

Misc. Tools

Ongage Deliverability Services

In Q2 2020 Ongage launched “Ongage Deliverability Services.” If your emails are landing in the SPAM folder, our deliverability expert team can help you turn that around, landing your emails in the inbox.

For more details see: