When emails end up in the spam folder, marketers are in no mood for joking. It is a serious issue that wounds both sender reputation and email deliverability. Let’s find out why emails land into the spam folder and how to maximize your email deliverability.

Authenticate your IP address with DKIM and SPF records

In September 2017, spam messages made up 59.33% of global email traffic. Mailbox providers are concerned about their level of security; therefore, they are addressing the issue with intensified sanctions against spam.

Spam Volume

That is why DKIM and SPF authentication is important: mailbox providers use these technologies to confirm the identity of the sender. If the latter cannot be authenticated, mailbox providers may reject the message or put it through additional filters to determine whether it should be delivered. Without authentication, the chances that your email will be filtered or blocked greatly increase.

DKIM (Domain Keys Identified Mail) is a method for validating domains through publicly available cryptographic signature. This signature is verified on the receiving end using the DNS record.

SPF (Sender Policy Framework) is used to compare the sender’s IP indicated in the domain’s DNS record with a list of IPs authorized to send from that domain.

How to check your DKIM and SPF records

You can use these tools to validate your DKIM and SPF records, check sender reputation, blacklist appearances and many other criteria:


These services work as follows: you send a test message to the indicated email address or type your IP address or domain into the form. Then you receive the report on the results for your domain, problem areas and proper operation, and correct configuration of your SPF, DKIM and DMARC records.

Monitor your sender reputation

When choosing a postmaster, consider which email client is used by the majority of your subscribers or set up postmasters of different mailbox providers. The following is the information you can check while using a postmaster:

  • Deliverability;
  • Compliant rate;
  • Delivery errors;
  • Reputation of sending domain and IP address.

You can also analyze other metrics in AOL, Gmail, Yahoo and Outlook postmasters.

Outlook postmaster

Choose an appropriate type of IP address

There are two types of IP addresses:

  • Shared IP address. These addresses are used by multiple senders, which increases the send frequency and volume, making the address warmed up. In this case, however, you cannot control the reputation of the address as it depends on the actions of other senders too.
  • Dedicated IP address. This address is used by a single sender, who is fully responsible for its reputation. A dedicated IP is a good choice if your monthly send volume amounts to more than 50,000 emails.

If you send bulk emails, it is recommended to register a separate address. For instance, one may be used for triggered emails and another for email campaigns. Take a look at the example from Mud Pie.

alternative email adress

Keep your IP address warmed up

Send emails regularly, no less than 50,000 messages a month. If you have registered a new IP address and have not sent anything from it yet, warm it up gradually by sending small amounts of emails.

How to warm up your IP address

Imagine you need to send 60,000 emails. If you send such a huge amount at once, a receiving server will probably reject it. But you may divide your mailing list into six groups each consisting of 10,000 recipients. Send emails to the first group every day during the first week. For the second week, add another group of 10,000 users to your mailing list and so on. If your bounce rate becomes higher than 10% and complaint rate exceeds 0.1%, reduce your sending volume to 5,000 messages a day.

Look for your address on blacklists

You can use these tools:

Analyze delivery errors

Delivery errors are divided into two groups:

Soft bounces

These usually result from temporary causes:

  • Full recipient’s mailbox;
  • Technical issues on receiving mail transfer agent;
  • Big email size.

Hard bounces

They arise due to the following reasons:

  • Nonexistent mailbox domain;
  • Syntax error in email address;
  • Mail transfer agent (MTA), spam filter or MTA protection software have identified your content as spam. In this specific case, you need to revise your email layout and content.

When hard bounce rate reaches 5%, the mail server blocks the sender.

In case that an email is bounced, the recipient’s server sends back a message with a three-digit delivery error code and a description of the reason for the bounce. To understand why your email can’t reach the recipient, keep at hand the enhanced set of delivery error status codes along with their meaning.

Use permission based marketing

Email campaigns cannot be sent without the expressed permission of receivers. This is a violation of the CAN-SPAM Act.

When you can send emails:

  • Users have subscribed to your emails on your online store or website. But, if a user has created an account or bought anything from your online store, you should ask for permission to send them emails.
  • People subscribed to receive your emails at your stand during an exhibition.

When you cannot send emails:

  • A mailing list was bought or rented from a seller with a good reputation.
  • Email addresses belong to participants of exhibitions or conferences. This is not a legal mailing list, no matter what sponsors tell you.
  • You have a list of members of your organization / followers / Facebook fans which, you think, will do. This is not a legal mailing list either. You can use it only if you have received permission to send them emails.

When you may send emails but should be alert to the nuances:

  • People have subscribed on your website or online store, but you have not emailed them for a while. There is a chance that they have forgotten you, so it’s better to start with a request to re-subscribe.
  • You have a list of users who have registered on your website / forum and agreed to the Privacy Policy. For your sending to be legal, these users should tick a box stating that they agree to receive emails from you.

Take a look at the full list of what is considered to be permission to send emails.

Use double opt-in

Marketers are still debating the optimal method for users to sign up for emails: single opt-in or double opt-in. Using a single opt-in, you ask a user to fill out a signup form and submit it. Double opt-in, in turn, presupposes that subscribers sign up via your signup form and then get an email with the link they have to click to confirm their willingness to to receive your emails. The second method works better for your email deliverability and inbox placement.

Double opt-in decreases the chance to end up in the spam folder

There will be no more nonexistent email addresses on the list. Only a real person using a valid email address can confirm the subscription. In case of single opt-in, however, some incorrectly typed email addresses may appear on your mailing list, for example, alex789@hotmai.com instead of alex789@hotmail.com. Besides, double opt-in method serves a good protection from possible tricks of your competitors. They simply won’t be able to enter invalid email addresses to spoil the quality of your mailing list.

Below you can see the example of the confirmation email.

confirmation of subscription

Verify email addresses on your mailing list

Invalid email addresses on your mailing list can result in high spam placement rate. Mailbox providers are more likely to block your sending IP address if you are ignoring repeated delivery errors and continue to send emails to invalid recipients. It’s a sound reason to establish and maintain good mailing list hygiene practices.

Email validators

Email validators will help you maintain a clean mailing list. Here are some of them:

Upload a list of email addresses from your computer or import your list directly from cloud services like Google Drive or Evernote. After your list is completely validated, you can download your report as a CSV or XLS file.

Explanation of the statuses returned by an email validator

  • Deliverable. This status means that recipients’ emails are valid.
  • Invalid. Email addresses do not exist for one of the reasons that will be detailed in the validation report.
  • Accept all. These email addresses can’t be fully validated. Such emails always return a valid status from some domains. Typically, these domains are trying to protect their legitimate users by telling the sending mail server they will accept the message for a given email address but then discarding the message or sending a bounce message instead.
  • Disposable. The addresses are created by users to be valid temporarily to sign up for promotions.The best option is to delete these addresses because they reduce your open rates and harm sender reputation.
  • Unknown. This status means that the recipient’s mail server is not responding. It can be a temporary status if the destination mail server is too slow or is not working.
  • Spam traps. These addresses are created by mailbox providers, filtering companies, and anti-spam services to be further spread through the web where they can be parsed. They are used to identify spammers or senders who bought their mailing lists or used illegal practices to collect addresses. Appearance of spam traps on your list is a reason for mailbox providers to filter your email to the spam folder.

Please note: Email validators can’t find all of the spam traps in your list. Therefore, the only hundred percent sure method to protect yourself from spam traps is to make the process of collecting email addresses organically and ethically.

mailing list verification

Reactivate sleepy subscribers

The higher your user engagement rate, the better your sender reputation is for mailbox providers.

Launch re-engagement campaigns regularly for subscribers who have not been active for a while. Firstly, determine subscribers who may be considered inactive, for example, those who have not opened and clicked your emails for three or six months. Then divide inactive users into those who have bought something from you and those who have not, and send these groups different reactivation campaigns.

There are different options for reactivation campaigns. For instance, you can provide a discount or a selection of the most interesting content of the last month. Below is an example of the re-engagement email by National Geographic, where subscribers are proposed to update their preferences.

re-engagement email

Pay attention to your content

Mailbox providers fight against spam using automatic filtering technologies. Some of them scan every part of your email to determine whether it must be marked as spam or delivered to the inbox. Among the elements which are checked there are the header, footer, HTML code, URLs, subject line, text-to-image ratio, attachments, spam words and more. As a result, filters can block up to 97% of all spam messages.

7 Don’ts for passing a spam filter successfully:

  • Don’t use shortened URLs or link redirections. Mailbox providers are watchful for these techniques as spammers often apply them to hide real links.
  • Don’t use complex codes: JavaScript, ActiveX, VBScript, Java applets, Frames and Iframes uploaded from external CSS, Meta Refresh websites.
  • Don’t use spam words in the subject line or within your email. There are many different lists of spam trigger words in the web, the most popular lately being blockchain, sale, price, free, etc.
  • Don’t overuse caps lock. Using all caps in the subject line is a game-over. Consider different copywriting formulas, psychological hacks or emoji to draw attention to your subject line.
  • Don’t overuse exclamation marks. Exclamation marks do not convey your excitement, but are rather a red flag for spam filters. Such subject lines resemble spam emails used to scam recipients.
  • Don’t neglect to check your HTML. Broken HTML can lead to a poorly rendered message and generate complaints. You can check your HTML for syntax and formatting errors using the Nu Html Checker.
  • Don’t overuse images. The common rule of thumb for email content is to maintain the 80/20 text-to-image ratio. Senders with a good reputation and highly engaged subscribers can, of course, afford to use more images. Stll, what is never forgiven by spam filters is an image-only email.

Where to check your email for spam-related issues

There are tools that can test your email for risky elements before you send it. They will scan your email for spam words and check the email layout.

Make it easy to unsubscribe

Make sure your unsubscribe link is easy to find and the process is simple. Do not bother subscribers who want to opt-out with unsubscribe surveys, do not redirect them to other pages, and do not ask for login and password to unsubscribe. People will flag an email with no regret if they can’t figure out how to unsubscribe in one click.

Test your campaign

Finally remember to do a test run of your campaign before emailing your whole mailing list to be on the safe side. Let your team take a fresh look at your email copy and fish out any errors. Alternatively, you may use an email testing checklist for an honest sending, spam, and email content testing.

Bottom line

To be sure that your email will make it to the inbox, use the following checklist:

  1. Maintain a consistent send volume. If your IP address is new, start slowly with a low send volume. Sending too many emails at once from an IP address that is not warmed up yet can be the reason for ending up in the spam folder.
  2. Make sure your SPF, DKIM and DMARC records are set up correctly.
  3. Collect a quality mailing list. Email only those who have given you permission to receive your messages. Sending emails to uninterested users puts your sender reputation at risk.
  4. Consider double opt-in as a subscription method.
  5. Pay attention to email content and layout, avoid spam-related elements.
  6. Include an unsubscribe link into your email and make it highly visible.
  7. Your email should state reason why a subscriber has received it. For example: You received this email because you are registered on…
  8. Check whether URLs and images you include into your emails are not blacklisted.
  9. Send only the relevant content and the content you’ve promised. If a user has subscribed to travel articles but suddenly receives recipes, your email is at risk of being marked as spam.
  10. Track delivery errors and complaint rate.

Be a good sender, pick up on the reasons of low deliverability and enjoy your email efficiency growing.

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