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Marketing 23 min read January 12, 2018

Complete Guide To Improving Your Email Deliverability

Complete Guide To Improving Your Email Deliverability
Picture by: Natalya Soroka
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Svetlana Maksimova
Editor at SendPulse
Do your emails often go anywhere but a subscriber's inbox? By reading this article, you'll find out three main causes of a poor email deliverability rate along with detailed suggestions on how to improve it.

Issues with sender's IP address

The quality of a sender's IP address impacts email deliverability much more than any other factor.

The following are possible problems with a sender's IP address:
No IP address authentication with properly configured DKIM/SPF, DMARC records. You can check yours using a dedicated service: Enter your domain name and DKIM selector and you will receive your SPF and DKIM values.
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Emails aren't sent from corporate domains, but from free email domains like,, and others.
Bad IP and domain reputation. Each recipient's reaction has a strong impact on your sending reputation. The calculation of your reputation includes such metrics as messages replied to, clicks on the links, complaint rate, "This isn't spam" rate and inbox placement rate. Having 100 opened emails out of 100 sent would be a greater contributor to your sender reputation than only 100 opened emails out of 1,000.

Among other parameters that influence your sending reputation, there are send volume, warmed up IP address, blacklist appearances, previous spam sent, number of delivery errors and further attempts to deliver the rejected messages.
Cold IP address due to irregular sending. Mailbox providers will reject a newsletter if you haven't been sending for months and then try to send out more than 10,000 emails at once.
Your traffic isn't segmented: promotional, transactional, corporate emails and newsletters are sending from the same IP address and domain resulting in overload.
Using an email service provider with a low rate, that isn't integrated with well-known email clients or doesn't have a registered SMTP server.

How to deal with these issues?

1. Choose an appropriate type of IP address

Dedicated IP address: is used by one sender or company. Nobody else has access to this address. Its reputation fully depends on the quality, volume, and consistency of emails sent from this IP address. If you control the process of creating and sending emails, and your monthly send volume amounts to more than 50,000 emails, we reccomend using a dedicated IP address.

If you send different types of email campaigns, you would be wise to use several IP addresses and register separate email addresses for each of them. For example, send informational emails from, while technical ones from

Shared IP address: is used by multiple senders. In this case, you cannot control the actions of other senders. You can only rely on their fair practices. Shared IP is a good option for those who send few campaigns with a frequency of less than 30 days. Thanks to the activity of other senders, such an IP address won't be considered cold.

It's best to register a separate IP address to send important email campaigns. This precautionary measure ensures higher deliverability. Moreover, other senders with lower reputations won't impact your sender score and create problems for you.

2. Warm up a new IP address

This point is relevant to senders who use a dedicated IP address. To keep the address warmed up, you should send at least 50,000 emails monthly. Remember, if you send such a huge quantity at once, a recipient's server would probably reject it. There are ways to work around that issue.

How to warm up your IP address:

  • Remove inactive subscribers from the list.
  • Divide your mailing list into five groups of 10,000 users each.
  • Send an email every day to the recipients in group one during the first week. For the second week, add another group to your mailing list.

If your bounce rate is higher than 10% and complaint rate exceeds 0,1%, reduce your send volume to 5,000 messages a day.

3. Configure authentication settings

Authentication is confirmation of a sender's IP address identity. Thanks to this process, the quantity of spam on the web was reduced by 7% during the period from 2014 to 2016. If you use a bulk email service provider or own a personal website, this procedure is essential to secure your brand and reputation.

If you send email campaigns from your personal server, configure DNS and the following essential types of authentication:

SPF (Sender Policy Framework). This is an email authentication protocol. SPF verifies the "from" address and compares it to the address indicated by the sender in the DNS record.

An SPF record contains information on email servers that are allowed to send emails and the sender's level of trust. This data enables email clients to determine whether the email can be accepted or not. You can find out how to create and set your SPF record in the SendPulse knowledge base.

DKIM (Domain Keys Identified Mail). This is a sender's authentication method that requires a cryptographic signature. Refer to the SendPulse knowledge base for a detailed guide on how to configure the DKIM record.

Transport Layer Security. This ensures a secure email delivery without snooping or data spoofing.

DMARC (Domain-based Message Authentication, Reporting & Conformance). This verifies the incoming emails of the given domain. Moreover, it determines what to do with email that doesn't pass the SPF/DKIM authentication, or what to do if a domain or sender's email address doesn't match the confirmed address. In this case, an email will be placed in the spam folder or simply won't be accepted. Thanks to DMARC, mailbox providers recognize emails from spoofed IP addresses that are disguised as senders with a good reputation.

4. Check your sender score regularly

Your IP address and domain obtain a certain score from your very first email campaign. If a domain has a high score, spam filters are more loyal to the content of the incoming email.

If the majority of your mailing list uses Gmail, you should track your sender reputation with dedicated online tools like Google Postmaster Tools. Once you have registered your IP address on Gmail Postmaster Tools, you can check the following parameters:
Spam rate
IP reputation
Domain reputation. Medium level is considered to be normal.
Feedback loop spam report
Verification of DKIM/SPF, DMARC records authentication
Encrypted traffic
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Delivery errors
Every large mailbox provider has similar tools available. It is recommended to use postmasters of those providers that the majority of your subscribers are registered with. You can carry out a general check of your sender reputation using SenderScore. A score higher than 65 is considered to be good.
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To check whether your domain is present on blacklists, you can use MXToolBox. This service provides a variety of tools to verify whether your domain, email server, and authentication settings are configured correctly.
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5. Sign up for feedback loop

Email clients don't inform senders when a recipient reports email as spam, so sign up for feedback loop (FBL). You (the sender) will receive a notification from mailbox providers containing information about who marked your email as spam and when, as well as which one. To be able to use this function, you should send a request. Feedback loops are available from AOL and Yahoo.

Here is an example of a feedback report from AOL.
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For this purpose, Gmail PostMaster has created a dedicated tool – Feedback Loop.

A feedback loop is an important and useful feature that helps you to take necessary measures to improve your sender score. For example, remove subscribers who complain from your mailing list, improve segmentation, or completely redo the content of your email. Some email service providers accept and process FBL reports from all available mailbox providers and subscribers are marked as "reported spam" in personal accounts.

6. Fill in the "From" address

Use a personalized sender's email address instead of standard role accounts like info@ or sales@. Usually, emails sent from role accounts get categorized into the "Promotions" folder in Gmail.

A well-known and permanent "from" address is more important for your deliverability than a subject line or preheader.
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Issues with a mailing list

Let's take a closer look at the different kinds of this issue:

No express permission to email

Email campaigns sent without the expressed permission of customers is a violation of the CAN-SPAM Act.

You cannot email:

  1. Participants of contests or workshops, unless they have agreed to receive your messages during registration.

  2. Members of groups or subscribers in social networks.

  3. Customers of online or retail stores, unless they have agreed to receive your messages in the application for a discount or during registration on a website.

No double opt-in form

To reduce the number of possible errors in email addresses, consider implementing double opt-in. It will also help you to ensure that emails will be sent to real people. A double opt-in process includes a confirmation step where the subscriber receives an email and has to confirm the subscription by clicking a link in the email.
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High complaint rate

Even engaged subscribers who receive relevant email campaigns can sometimes report it as spam. But if your complaint rate increases suddenly, that is quite a different story. In that case, you'd better review your email.

The following are possible reasons for complaints:

  1. Subscribers can't find the unsubscribe link, or it is simply not included. They will subsequently mark such email as spam in order to receive nothing else from the sender.

  2. Subscribers opt out but still receive emails, or the subscriber hasn't received a notification that unsubscribing will take several days. The time lag annoys recipients.

  3. The subscriber is required to visit their personal account on the website to unsubscribe.

  4. A customer wasn't informed about being subscribed to the newsletter. For example, there was no welcome email. In this case, your first email can be a surprise to him/her.

  5. Email content doesn't correspond to subscribers' expectations. For example, a recipient has subscribed to an educational email series, but instead, they receive transactional emails.

  6. Subscribers receive emails too often or too rarely. In the first case, subscribers are irritated by persistence, while in the second one, they have simply forgotten about opting in.

Numerous delivery errors

Delivery failures often happen for reasons that are beyond an email marketers control. This applies especially to soft bounces. The causes of soft bounces are as follows:

  • the subscriber's mailbox is full;
  • the mailbox hasn't been used for a long time;
  • the server is down.

Theoretically, a soft-bounced email can still be delivered once the problems are addressed.

Hard bounces, in turn, happen due to the following reasons:

  • nonexistent email address or recipient domain;
  • syntax errors in email addresses;
  • recipient's mail transfer agent blocked the delivery.

If you ignore repeated delivery errors to the same subscribers and don't remove such email addresses, your deliverability rate will decrease to 20%. The accepted level of soft and hard bounces that doesn't affect the sender's reputation is
2–3%. The best way to improve it is to use double opt-in and remove inactive addresses from your list every six months.

Email hits a spam trap

Spam traps are email addresses or domains that hadn't been used for more than 18 months and now belong to anti-spam services or internet service providers. Sending emails to such recipients can significantly impact your sender reputation. The sender who ends up in the trap is automatically flagged as a spammer, even if it isn't so.

The theory is that validators and verifiers of mailing lists can help you to avoid spam traps, but that doesn't correspond to reality.

Emails go to unengaged subscribers

Email clients track user activity. Based on these observations, they decide whether to accept or reject an email. This relates in particular to Yahoo, Gmail, Microsoft, and AOL. For example with the last one, emails often don't even get to the spam folder, not to mention the recipient's inbox.

When assessing audience engagement, email clients consider the following:

  1. The percentage of emails read. The more emails that are read, the higher are the chances that the subscriber is interested in your email campaigns.

  2. The number of emails marked as not spam or those moved to the inbox folder. For example, Gmail considers this to be a sign that the email campaigns are desired.

  3. The quantity of emails forwarded is another indicator that subscribers value your emails and are ready to share them.

  4. Emails replied to. This relates to personal emails.

  5. Senders added to contacts. If subscribers trust these addresses, emails incoming from them can be placed in the inbox.

  6. Emails deleted without reading. This is a clear sign which emails are interesting for subscribers and which are not.

Most of these metrics are unavailable for analysis, as mailbox providers hide them. They don't disclose this information publicly; otherwise, spammers would quickly find a way to override it. Therefore, consider the activity of your subscribers outside of the email campaign: past purchases, downloads, activity on the website, and browsed pages.

How to deal with these issues?

1. Avoid spam traps

The following are types of spam traps:

Recycled. These addresses once belonged to a real person but became abandoned. If you send email to such an address, you will receive error message 550: invalid recipient. Repeatedly sending to these addresses worsen your sender reputation, so remove them from the list ASAP.

Pristine spam traps or honeypots. These addresses are published on public websites and are created solely to capture spammers and senders with low-quality mailing lists. A double opt-in form is the best way not to end up in these types of spam traps.

Syntax errors and typos in domain names. Examples of this are or No matter whether a user misspelled it or it was an error of the email marketer who collected the addresses, sending to mistaken recipients will significantly reduce your deliverability rate.

2. Collect a quality mailing list

Send newsletters to users who are actively engaged with your information. In this way, you can maintain a high deliverability rate.

This requires the following actions:

  1. Ensure that email addresses of new subscribers are valid. Don't rush to send a welcome email in order to avoid hard bounces.

  2. Use a double opt-in form.

  3. Set expectations in your subscription form or welcome email; review your email frequency and the content subscribers will receive.

3. Email your list regularly

If you have collected your mailing list with due diligence and have sent a welcome email immediately, sending your next email after several months would be a huge mistake. Your subscribers might not recognize you and mark your email as spam. Keep sending regularly, for example at one-week intervals. You can also let your subscribers know about the frequency of your email campaigns.

4. Monitor subscribers' activity

Inactive addresses can mask subscribers who are no longer interested in your emails or are spam traps. If you send email campaigns once a week, and subscribers don't open or click the links for two months, it makes sense to check their past website activity or purchases. You can send such subscribers a reactivation email like busuu does, an online community for learning a language.
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You should run a reactivation campaign within a maximum period of six months. If you have put your reactivation campaign on the back burner, remove inactive addresses from your mailing list so as not to risk your sender reputation.

Issues with email content

Email clients carefully observe email content by keywords and links to URLs present in blacklists. Then they decide where the email should be placed. Presence of spam words guarantees that the email will go directly to the spam folder. Only an ideal sender reputation or highly engaged users can save you from this.

The following are possible problems with email content:

  • Email contains more images than text. Your email is a single large image.
  • Email programming code is broken or complex – PHP, JavaScript, Java, ActiveX, ASP.
  • Links lead to domains that are blacklisted.
  • There are spam words in subject line or email text.
  • Email contains files for download instead of links.
  • Email size is too large due to visual elements.
If you have discovered your emails have one or more problems from this list, keep reading. We will tell how to remedy this issue.

How to deal with these issues?

1. Avoid spam words, excess punctuation and uppercase letters in your subject line

If you have composed your subject line using spammy methods to attract attention, then spam filters can simply block your message. Even if such an email avoids the spam folder and is filtered to an inbox, it may look like spam to your subscribers. Especially if your subject line contains such words and phrases as "risk-free," "Act now!", "FREE!!!", "Make $" and so on. Below you can see a clear illustration of subject lines that were filtered into the spam folder.
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The overuse of exclamation points, special symbols, and caps lock is also a trigger for spam filters. Relevant content, creative ideas, facts, humor, and intrigue attract subscribers' attention much better. And one more thing to keep in mind: your subject line should correspond to the email content.

2. Watch your email structure

Always add the unsubscribe link. If a subscriber is no longer interested in your email, give them a chance to unsubscribe. That is better than moving your email to the spam folder leading to a damaged delivery rate.

Add a link to your preference center. Your subscribers will have the opportunity to indicate the content they'd like to receive, email frequency and get unsubscribed. Below is an example of the preference center from Mud Pie. A link to it is in the footer of every email. It is a good practice, as it helps to segment the list, and, as a result, to send relevant content.
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Verify the HTML-code of your template. Any errors in your code can trigger the majority of spam filters. Don't forget to test how your email is rendered on different devices and in various browsers. Don't use complex codes like frame, PHP, JavaScript, Java, ActiveX, ASP and cache boosters.

Include both plain text and web versions of your email. If visual elements aren't displayed, subscribers will still be able to review your email. Moreover, spam filters are more loyal to such messages.

When you add links to your email, create a call-to-action button or anchor link with appropriate text instead of shortening it.

3. Improve email content

Keep your text-to-image ratio within 80 to 20. If your sender reputation is good and your IP address is warmed up, you can use more images. Don't create emails as a single large image, and always title them with alt-text.

Files for downloading should be provided as links instead of attachments. Emails with embedded attachments along with large visual elements are more likely to end up in a spam folder.

Check all the links to make sure they aren't on blacklists. If the link leads to an external source, check it for reliability and authenticity. Never engage spammers to promote your website, as it will negatively impact your deliverability rate.

4. Check email content using anti-spam tools

Bulk email services provide features to test email content for spam, but you can always scan your email additionally using online tools.

Check your email for the following points before sending:

  1. Bad HTML code in your template;
  2. Image-to-text ratio;
  3. Quality of URLs and IP addresses;
  4. Missing the unsubscribe link;
  5. Inclusion of spam words.

Bottom line

Three key pillars of good deliverability are a high sender reputation, a quality mailing list, and quality email content.

The following are a summary of the suggestions to avoid ending up in a spam folder:
If you are sending more than 50,000 emails per month, use a dedicated IP address. If your monthly send volume is less than 50,000, a shared IP address is a better option.
Email your list regularly and maintain a consistent send volume to keep your IP address warmed up.
Set up DKIM/SPF, DMARC authentication.
Track your sender reputation using postmasters of mailbox providers.
Use a dedicated mailbox on your corporate domain for email campaigns. If you send different types of messages, establish a mailbox for each separate type of email.
Send emails to those who have given you their permission.
Use double opt-in.
Purge your list regularly of inactive subscribers. Launch re-engagement campaigns if needed.
Don't use spam words, complex code and large images.
Provide an unsubscribe link and opportunity to update email preferences.
Check email content using anti-spam tools.
Follow our recommendations to improve your deliverability and email marketing ROI.

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