Email Deliverability Tips

Email is one of the most effective marketing channels for revenue generation and email deliverability is extremely relevant to the success of your email campaigns. Its objective is for the email to reach the customer’s inbox. Major Inbox Providers (such as Gmail or Yahoo) have processes defining a good email sender, determining whether the objective will or will not be fulfilled.

In this guide you will find:

  • What are the deliverability factors
  • Tips - what to do
  • Tips - what to avoid doing

Deliverability factors

Deliverability factors influence whether the email will be successfully delivered to your customer's inbox instead of for instance the e-mails getting blocked or delivered straight to the customer’s spam folder. Experimenting with these elements is entirely within your control. Some of them have a big impact on deliverability, while others aren’t as important as you might think. The four main factors are:

1. Quality/health of your contact lists

This is always important, but if you’re a new sender, or your IP is new, this is all the ISP knows about you.

Have a look at the article about the health of your email list to learn to effectively segment your email list in Bloomreach Engagement to keep it healthy and of high quality.

2. Frequency and relevance of e-mails

If you send emails every day, ISPs will be stricter with you. You absolutely need to segment your mailing list in this case. Are you sending the same message to everyone? Are you personalizing content? This will have a big impact on engagement and thus deliverability.

Do not send too many emails. Have only the most engaged audience receiving the highest frequency of emails. An example is listed below. More emails don't necessarily mean more effective email campaigns.

Choose quality over quantity. It is vital to prefer the quality of emails in your list over their quantity. Even though it may seem counterintuitive, the approach of sending emails to as many addresses as possible will result in lower click/open rates, therefore decreasing your sender reputation.

3. Content and format of the email

This matters, but not as much as some would believe. Spammy messages from a sender with a high reputation will have fewer deliverability issues than valuable messages from a sender with a poor reputation. Nevertheless, it’s good to avoid using spammy tactics.

4. Sender reputation

Sender reputation is extremely important, but not quite as in your control as the other above factors. It deserves more attention. Watch the video offered by the Bloomreach Academy to learn some of the best practices and read our further tips to maximize your sender reputation even more.


Sign up for the Mini Masterclass

Decrease spam landing, tackle deliverability challenges and much more with bite-sized videos available for free in the Engagement Mini Masterclass. For even more tips read our blog.

The Mini Masterclass also offers specific videos giving you tips on how to improve your emailing techniques during Black Friday so that you make most out of the peak seasons!

Email deliverability do’s and don’ts

We’ve compiled a list of some of the most important dos and don’ts of email deliverability. Check and see if you’re following emailing best practices, and get some ideas on where you can improve.

If you follow our tips, you should greatly increase the chances of your emails making it to your inbox. An added benefit is that your emails should be more relevant, and the customers that get them will be more engaged with them – a win-win situation.

TIPS - What to do?

  • Fulfill necessary technical requirements

    In order to become a reliable sender, you need to comply with a series of validation reports (SPF, DKIM), which essentially confirm that the email sender's domain is linked to your domain. This is a requirement for all of the Bloomreach Engagement clients.

  • Verify your domain

    It is recommended to verify your domain with your ISPs right at the same time as fulfilling the technical requirements mentioned above. This will not directly help your email deliverability, but it is very helpful for identifying deliverability issues and for troubleshooting. Together with the verification of your domain, you will have access to ISP tools, which will provide you with information about the reputation of your domain and your IP addresses. It is recommended to check the data once in a while. These tools vary depending on the ISP. Here are links for a few of the major providers.
    - Google - Postmaster, What is Postmaster?, Verify your domain.
    - Yahoo - Feedback Loop
    - Microsoft - Microsoft SNDS (Smart Network Data Services).

  • Segment your mailing list

    To see how to manage your email database, see the article about the health of your email list.


Avoid spam traps

Spam traps are inactive email addresses. They can be created by spambots as mentioned above, or they can be just addresses that are not used anymore. Sending emails to these addresses extremely damages your deliverability reputation. Fortunately, we have a feature Suppression lists to help with that.

  • Check the sender guidelines of your ISPs

    They may include many concepts already mentioned here, but it is preferred to go through them and make sure you comply with them. Every ISP tends to have its own, for instance Gmail guidelines or Yahoo guidelines.

  • Ensure that your email renders for everyone

    Bloomreach Engagement can help you test how your email will render across devices, apps, and browsers. Have a look at our Email previews feature. Emails that don’t render properly can result in no engagement or spam complaints. Emails that render correctly also increase your trustworthiness in the eyes of the ISPs.

  • Be careful about the content of your emails

    Score your content using spam checking tools, available also online and free of charge. Furthermore, be aware of the size of the email. In Bloomreach Engagement, a feature will notify you when the size surpasses 102 KB, which is the maximum recommended size.

  • Use personalization

    Personalization increases engagement rates, which is good for your sender reputation and your revenue. Reduce the batch and blast campaigns as much as possible. In other words, sending the same email to the whole mailing list is not the preferred strategy. The more you can tailor the email to the individual customer, and go beyond just using first names. Incorporate things like behavioral data, purchase data, and user preferences. Here is an article about a personalized subject line to get you started.

  • Maintain a proper text-to-image ratio

    60:40 in favor of text is a sensible guideline, although taking into account the attractiveness of the visual aspect, 50:50 is acceptable as well.

  • Make your sign-up process memorable

    People who remember signing up for your emails are less likely to report you as spam, which will result in a better sender reputation.

  • Double opt-in is highly recommended

    Similarly, if the customer confirms their interest, the likelihood of their reporting your email as spam significantly decreases. Furthermore, you will also avoid hitting spam traps. Check out our Double opt-in business use case article. A good double opt-in program should have a 70% success rate.


Bloomreach Engagement can help you with an out-of-the-box Plug & Play Double opt-in scenario, please contact your CSM if you are interested!

  • Include CAPTCHA to prevent spam bots from signing up to your list

    Spambots may attack your sign-up, resulting in filling up your email list with artificially created email addresses.

  • Make the unsubscribe process as easy as possible

    If someone doesn’t want to receive your emails, let them opt out as easily as possible. This way, they won’t report you as spam and therefore your sender reputation won’t be damaged. See also List unsubscribe article about our feature making the unsubscribe process even easier.

  • Review your campaign reports at an ISP level

    Monitor bounce and complaint rates at an ISP level and look for signs (dips in open/click rates) of your emails being bulk sent to spam for certain ISPs. This is something you want to avoid, as it significantly decreases your sender reputation.
    Oftentimes, if you use good emailing practices, the dips in open/click rates may be happening only on a specific ISP, therefore it is beneficial to be able to know where the blocking of emails is happening for further analysis of the problem. This can be done using an email domain report.

  • Check blocklists

    It is recommended to check whether you are to be found on a blocklist. That would prevent your emails from reaching the inbox of the customer.
    Here is a tool you can use for this purpose: Blocklist check.

  • Precedence: bulk

    The "Precedence" email header is used to classify emails based on their type by ISPs. It is important to have the precedence set to bulk (indicating that the email is sent to many people). Otherwise, it is more likely that the ISPs will direct your message to the recipient's spam folder.


In Bloomreach Engagement, you need to check the box for the usage of bulk settings as shown in the picture. The checkbox may be found while creating an email campaign (either directly through "Email campaigns" or "Scenarios" ) under "Design>Settings".

TIPS - What to avoid doing?

  • Don’t buy, rent or harvest e-mail addresses

    You absolutely need to know the quality of your mailing list. If you’re buying addresses in bulk, it’s very difficult to know exactly what you’re getting. Plus, this can be a violation of guidelines like the GDPR.

  • Don’t send emails to people who don’t want them or cannot receive them

    This can also put you in violation of the GDPR, and it’s likely to get you more spam complaints.

  • Don’t send emails to users who have not opted-in

    First and foremost, GDPR prohibits you to do so. In addition, it would significantly drive up spam complaints and destroy your sender reputation.

  • Don’t send emails to old or inactive addresses

    These customers aren’t adding any revenue to your business, and they’re hurting your metrics. It’s a good idea to cut off any email addresses that have no engagement within the last 180 days – transfer these accounts to a re-engagement (or even a re-permission) program. You can also use our Email List Hygiene Filter to automatically block sending of emails to inactive addresses.

  • Don’t use spammy language

    USING ALL CAPS, ending sentences with lots of punctuation (!!!), using too much “super-hot exclusive sale!” terminology… the ISPs don’t like any of it, and neither do your customers.

  • Don’t send too many emails

    We recommend sticking with the convention of not sending more than one email per day. Furthermore, adjust your email frequency to email engagement. Only your most engaged audiences should receive the most emails. You can use list segmentation to help manage this or our built-in Frequency policies. The reduction of the frequency of emails is a proven tactic for re-engaging a less engaged audience. Here is an example of how that could be divided.

People whose last open or click is in the last 30 days3+ emails a week
People whose last open or click is between 31 and 90 days2 emails a week
People whose last open or click is between 91 and 180 days1 email a week


Advanced strategies

Read our blog about Email marketing analytics about metrics, KPIs, and reports.