Email Deliverability Best Practices

Email Deliverability Best Practices

Let's be honest: email marketing is nothing without deliverability. Don't believe anyone telling you otherwise. If your email is delivered, it can be seen, read, and clicked on. And if you can increase your email deliverability by even just 2-3%, it can significantly increase your ROI.

But considering smart filtering systems employed by mailbox and Internet service providers, achieving high deliverability rates is not easy.

Using this email spam checker tool you can test each email you are about to send to your list and see how it is treated by different mailbox providers and where it is delivered: Inbox or Spam.

In the modern world, email deliverability is determined by sender reputation, bounce and complaint rates, and recipient engagement.

To keep all these factors in order, you need to follow these four email marketing practices:

1. Use Good List Acquisition and Management Methods

Ideally, your email list must contain exclusively the email addresses of the recipients who are engaged with your brand and want to receive your messages. In the reality, email marketers often use poor list building and management methods.

However, it's important to strive for the "ideal" list because the quality of the email list impacts deliverability tremendously. Mailbox providers monitor the email addresses to which you are sending emails and will filter or block your messages altogether if a poor list quality is determined.

Thus, to be on the safe side, consider the following best practices when it comes to list building and management:

#1. Do Not Buy or Harvest Email Addresses.

Buying or harvesting email addresses from public sources seems to be the easiest and quickest way to populate the email database.

But it's a bad practice for these four reasons:

Unsolicited emails

If your recipients don't know who you are or never subscribed to receive your mailings, your emails could look like spam to them.

After enough of spam complaints, your sender reputation will go down, and ISPs will start filtering your emails. Even worse, you could have your IP landed on a blacklist, ultimately making it harder for your future campaigns to be delivered to people who actually want to hear from you.

Needless to say, sending to email recipients who haven't opted in is illegal in many countries and violates the CAN-SPAM Act.

Hard bounce addresses

You can't always trust the quality of a purchased list. You don't know where those addresses came from, whether or not they are correctly formatted and valid. The mailbox might have never existed, or has been terminated by the mailbox provider, or abandoned by the end user.

Thus, purchased or harvested email lists are likely to generate a high hard bounce rate. Mailbox providers ask senders to have low hard bounce rates because it shows that you manage your email lists and keep them up-to-date.

Bounce rates above 10% will likely cause deliverability issues. Ideally, you should keep your bounce rate below 2% to achieve a high Inbox placement.

Spam traps

Spam traps are email addresses that don't belong to active users and are created and used by mailbox providers, anti-spam organizations, and blacklist administrators to identify spammers and senders using poor data management practices.

When a mailbox provider sees spam traps hits from a particular sender, they question the sender's list quality. Then they place verdicts on the sender's IP address, domain, or content, which then allow them or filtering companies to take measures such as temporary or permanently blocking the sender's email.

The type and age of the spam trap often influence the severity of verdicts placed on senders who hit spam traps.

There are two types of spam traps:

Recycled spam trap: it is an email address that once belonged to a real person, but was turned into a spam trap after being abandoned. Recycled spam traps are aimed to identify legitimate senders with poor list hygiene practices.

Pristine spam trap: also called "honey pots," it is an email address set up solely to capture bad senders and was never owned by a live person. It is assumed that no one should send an email to such an address.

Many spam trap managers hide their spam trap addresses on websites, so only harvester tools can capture them. When senders harvest email addresses from websites, they get spam traps. Any email sent to such addresses is seen as spam.

Bad statistics

This is obvious. Those people didn't want to hear from you, so what's the reason for them to open and read your message. At best, very few of them will open and click your emails. Are those few email clicks worth spoiling reputation and future deliverability?

Not to mention, your sending costs are increasing as far as your email list is growing. With a bad list, you are paying more and getting less. The key is to have a list of valid and engaged subscribers who want to receive your emails and act on them positively.

How to achieve that? Read below…

#2. Employ Good List Management Practices.

Following are the recommendations for keeping hard bounce emails, complaining users, and spam traps away from your email list:

Use confirmed opt-in.

Marketers who ask people to take an action — usually click a link — to confirm their subscription generally generate smaller lists than those who don't ask anything, but those lists are much cleaner than non-confirmed lists. They also used to have lower complaint rates.

Quarantine new addresses.

If you don't use a confirmed opt-in process, don't email new subscribers until you send a welcome message and do not receive a hard bounce. This protects you from adding invalid addresses to your regular subscriber base.

Provide easy update/unsubscribe options.

People often change email addresses and may be willing to update their contact information with you. If you don't have a full preference center, offer the option to change the email address at the point of unsubscribing.

Send regularly.

As a rule, the less often you email your list, the more likely you are to have high bounce rates. "Frozen" email lists are also more likely to produce spam hits as old addresses may have been turned into traps since your last campaign.

Handle bounce, complaints and unsubscribes.

Usually, these are handled by the email service provider, but if you are operating a self-managed email system, you should set up the process of handling them yourself or use a 3rd tool like GlockApps.

GlockApps will provide you with daily reports about your bounces and complaints. You will only need to load them into your "do not send list" or suppress those addresses from your base forever. As to unsubscribes, most self-hosted email solutions offer the unsubscribe handling as a feature.

Read:  How GlockApps Helps Emails Reach Their Inbox Destination

Monitor inactive users.

According to the best email practices, a subscriber who has been inactive for more than a year and has not responded to your re-engagement campaigns should be removed from your list. Set shorter "inactivity" periods of six-nine months if you send frequently and separate passive recipients from your main list.

Note: do not delete inactive users forever. Just keep them separately and stop sending email campaigns to them. Though they do not respond to your email communications, you can always try to reach them through other channels, for example, social networks.

Scrub and validate your list.

Regularly check your list for role accounts (, obviously bogus addresses (, and typos (

If you allowed your list to "freeze," consider checking it for validity before launching a marketing campaign. Use desktop email verifier or online email validation services like BriteVerify or DataValidation to determine invalid users on your list.

Verify your sender domain.

Domain verification is an essential step for deliverability improvement. It is a way of proving that you own the domain you send emails from, ensuring that no one else is using it. Verifying your domain is especially useful if you send emails from different addresses that belong to one domain.

Segment your email list by engagement.

Segmenting has proven to be useful for many reasons. One can segment the audience according to age, location, profession, etc. Segmenting your email list according to the recipients’ engagement is basically dividing clients into groups according to the frequency of opening and clicking through your emails.

When you have engagement-based segments, you can leverage them to improve sender reputation and deliverability, create campaigns for highly-engaged audiences, and specific strategies for re-engaging inactive recipients.

Authenticate your emails.

It is a must for a 21st-century email marketing. By authenticating you verify that the emails you send are actually sent from you and that your email was not altered on its way to the recipient. This procedure protects your brand and your customers from phishing and spoofing.

2. Set up Good Sending Infrastructure

You can’t send successful email campaigns and achieve high Inbox deliverability if you have a weak email sending infrastructure.

If you’re serious about email marketing and are going to run world-class email campaigns, you must have a robust infrastructure providing accurate authentication, high sender score, clean sending IP address, and a good sender domain/email reputation.


Let's consider the main components of the sending infrastructure and their impact on email deliverability.

#1. Email Authentication.

Authentication allows the mailbox provider to confirm that the sender is the one who he pretends to be. If the sender cannot be authenticated, then mailbox providers may block the message or run it through additional filters to determine whether it should be delivered (and where) or not.

There are four primary methods of authentication:

1. SPF (Sender Policy Framework). SPF is an open standard created to stop forgery of "From" addresses. SPF records allow the receiver's host to verify that the email is being sent from the server it asserts it's sent from. It's like the email sender is telling the receiver "I send emails from this computer only."

So, if any other machine tries to send an email from the same domain, the receiver's mail server knows the "From" email address is forged. SPF standard is being used by a number of ISPs including several large mailbox providers such as Hotmail, Yahoo, AOL, etc. and mail hosts.

2. Reverse DNS. This is another way to authenticate the email sender to the receiver host. Reverse DNS lookup implies determining what host and domain name belong to a given IP address. If a Reverse DNS Lookup returns a "no domain associated", then the email will likely bounce to the sender, or will be deleted or filtered.

3. DKIM. This is the next step to do after you setup your Reverse DNS records. According to Wikipedia, "DomainKeys Identified Mail (DKIM) is an email validation system designed to detect email spoofing by providing a mechanism to allow receiving mail exchangers to check that incoming mail from a domain is authorized by that domain's administrators and that the email (including attachments) has not been modified during transport."

In other words, DKIM authentication system checks if the email is actually sent from the domain it claims to be sent from.

For legitimate senders, authentication is essential because it:

– Protects your brand against phishing and spoofing.

– Builds your domain reputation.

– Reduces the chances of the messages being filtered or blocked by major mailbox providers and increases the Inbox Placement rate.

– Allows you to sign up for Yahoo feedback loops. Yahoo feedback loops are domain based and require senders sign their messages with DKIM to sign up for the program and receive complaint feedback.

4. DMARC. DMARC ensures that the legitimate email is properly authenticating against established DKIM and SPF standards, and that fraudulent activity appearing to come from domains under the organization’s control (active sending domains, non-sending domains, and defensively registered domains) is blocked. Two key values of DMARC are domain alignment and reporting.

DMARC’s alignment feature prevents spoofing of the header “From” address by:

– matching the header “From” domain name with the envelope “From” domain name used during an SPF check, and

– matching the header “From” domain name with the “d= domain name” in the DKIM signature.

Here you can read the complete guide about email authentication.


Authentication is not the magic formula for solving deliverability problems. While it will make it harder for your "From" domain/email to be forged, it will not compensate for poor list management and sending practices.

#2. IP Address.

An IP address is a number in the domain name system that sends email on behalf of your domain name. Mailbox providers look at the reputation of IP addresses sending emails on the behalf of your domains when deciding whether or not to put your email in the Inbox.

There are two types of IP addresses that email marketers can use:

Dedicated IP Address

It is used by a single sender. It means that no other marketer or company is sending an email from this IP address. The IP address reputation is affected only by the sending practices of the IP owner.

Shared IP Address

It is used by multiple marketers or companies to send emails. The overall reputation of that IP address is evaluated based on all messages sent by all the IP address users. Thus, the IP address reputation can be spoiled by one sender and then all senders sharing the IP will be negatively affected.

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Best email marketing practices teach that senders should have a dedicated IP address to maintain full control over the mailing activity associated with the IP address. However, when you are using an email service provider, you are sharing the IP and reputation with other ESP users.

If you are concerned about your reputation, you can consider a hybrid email system like EasyMail7. Hybrid email software works as a front-end to delivery services and SMTP relays. So, you can get a dedicated SMTP server with a dedicated IP address and use it with the hybrid email system. This way, only you will be responsible for your email traffic and IP reputation.

On our opinion, email marketers should look for a dedicated IP address in case they are planning to send high volumes of emails. If you are one of them, you will need to “warm up” your IP by starting with small mailings and increasing the volume slowly over time.

A good scenario of the IP warm up is:

Day 1 – 1000 relays per day and 100 per hour
Day 2 – 2500 relays per day and 200 per hour
Day 3 – 3500 relays per day and 300 per hour
Day 4 – 4500 relays per day and no hourly limit
Day 5 – 7500 relays per day and no hourly limit
Day 6 – 9000 relays per day and no hourly limit
Day 7+ – no limits

If you are using G-Lock EasyMail7, you can set the limitations per hour and per day in the Outgoing Mail Account settings to be sure you are not exceeding the volume of sent messages each day.

It’s also important to watch the bounce rate and complaint and if any of them or both are high, you should stop mailings and fix the issues causing a high bounce/complaint rate in order not to spoil your IP reputation.

When you are using an email service provider like MailChimp or delivery service like Amazon SES, Mailgun, SparkPost or others, you are sharing the IP and reputation with other ESP users. ESP and delivery vendors already have good “warmed up” IPs and are known to provide high deliverability to their users. At the same time, they are severe towards bounce and complaint rate and will suspend your account if your bounce and/or complaint rate exceed the allowed threshold.

It's always a good idea to check the reputation of the IP address you are sending emails from. Return Path offers a tool called Sender Score. The lower your Sender Score, the worse it is for your reputation at that IP address. Plus, you can see your Sender Score at GlockApps.

G-Lock Apps sender score

Your Sender Score is an indication of Inbox potential, but it's only one of many factors mailbox providers look at when determining the destiny of the emails.

ISPs are forced to introduce filters and blacklists to protect their users from unsolicited emails. Thus, besides public blacklists, your sending IP can be blocked by a particular ISP like Gmail, Hotmail, Yahoo or other which makes it a real problem to get your emails delivered to target recipients at that ISP.

Below are good guides you’ll want to check to learn how to find out if your sending IP is blacklisted by an ISP and how to request the removal:

How to Remove Your IP Address from Gmail’s Blacklist
How to Remove Your IP Address from the Hotmail/Outlook’s Blacklist
How to Remove Your IP Address from the Yahoo!’s Blacklist

The next important thing related to the IP address many marketers forget about is sending frequency.

Sending frequency relates to the mailing history of an IP address. After the change of an IP address, many marketers start sending emails to their entire list immediately without thinking of consequences.

Since a new IP address has no reputation yet and because spammers often use random IP addresses to send large quantities of emails, mailbox providers will restrict the number of emails they will accept from a new IP address (it is called "throttling") and often filter email into the junk folder until they monitor a consistent legitimate email volume sent from the IP address. Once consistency is seen, throttling is either reduced or removed.

Here are a few tips to keep in mind regarding the IP address and sending frequency:

1. Don't jump from one IP address to another.

Spammers tend to maintain a large pool of IP addresses rotating them during email sending to trick the system. But this technique puts you at risk of being blacklisted.

2. "Warm up" your new IP address.

After you've got a new IP, it's important to start sending slowly with a low email volume to establish an IP address reputation. Over time, you can increase the volume.

3. Be consistent at sending.

Mailbox providers used to filter email when sudden boosts in volume happen. Once you achieve a positive reputation on an IP address, try to maintain a consistent email volume. Senders with inconsistent mailings (for example, seasonal businesses, timed for holidays campaigns) will need to utilize some additional strategies to achieve sending permanence.

4. Check your IP against blacklists.

Today there are over 300 available blacklists, ranging from public well-known and widely used lists to privately held ones.

There are two main types of public blacklists: IP address-based and domain-based.

IP address-based are lists of IP addresses that can be queried in real-time. Some of them include (SBL), (XBL), (CBL), Return Path Reputation Network Blacklist (RNBL), SpamCop (SCBL),,

Domain-based are lists of domain names that appear within the email body. A filtering system will look at the URLs within the body of the email to see if they contain a domain that has been identified as a source of spam. The most commonly used domain-based blacklists are, URIBL, SURBL.

Blacklists can be a serious barrier on the path of the email to the Inbox. Using GlockApps IP reputation monitor, you can check your IP address against dozens of blacklists on auto-pilot and be notified if any blacklisting issue is observed.

 G-Lock Apps IP reputation monitor

If you find your IP listed on a blacklist, take time to find out and resolve the root problem that caused you to be blacklisted and then submit a delisting request.

If you do not resolve the problem, you'll be listed again, and over time your delisting requests can be rejected.

#3. Domain/Email Address.

A domain name is the registered name on the Internet (for example, A domain reputation is the sending reputation for the domain name.

Like authentication and IP address, a domain reputation is a factor that is evaluated by ISPs and mailbox providers and taken into account when they decide where to place the email.

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When determining a domain reputation, these metrics are used:

– Spam placements: how many times emails from the domain went into the spam folder due to the IP address reputation or content filters.

– Inbox placements: how many times email from the domain went into the Inbox.

– Complaints: how many times a recipient marked messages from the domain as spam.

– "This is not spam" markings: how many times a recipient found the message sent from the domain in the junk folder and marked it as "not spam."

Some mailbox providers can have more tight filters and evaluate the reputation of the email address the email is sent from which is determined based on the same metrics as the reputation of the domain.

Sometimes, it may be enough to change the sending domain or email address to see the improvement in the deliverability. If it helps, you should apply best email marketing practices outlined in this post to build a good reputation for your new domain/email address.


It's time to talk about the last but not the least factor that impacts email deliverability which is engagement. Some marketers having a healthy email list and good sending infrastructure still find their email messages delivered to the spam folder. It is most likely due to a poor subscriber engagement.

3. Keep Your Recipients Engaged, for Best Deliverability

Engagement can be defined as a positive interaction of a recipient with email messages: opens, clicks, replies, forwards, "not spam" markings.

Engagement is also an essential factor in filtering. Thus, every marketer should strive for keeping an engaged subscriber base — people who like receiving their emails, who open them regularly, and interact with the content.

How do mailbox providers evaluate subscriber engagement?

Each provider has its own criteria for measuring engagement. Some are more advanced than others, but all do evaluate subscriber engagement to make Inbox/Spam placement decisions. Microsoft, AOL, Gmail, and Yahoo are the industry leaders in their use of engagement metrics to determine email placement.

The most important metrics are:

>Message is read – a positive indicator that the recipient wants to receive your emails.

Message is replied to – a positive indicator that the message is desired and presents a personal interest to the recipient.

Message is forwarded – a positive indicator that the recipient finds the message valuable and thinks that others should see it, too.

Message is marked as "not spam" – a very strong positive indicator that mailbox providers use to train their spam filters.

Message is moved to a folder – an indication that the recipient wants your email, but also wants to better organize it and access it later.

Sender/domain is added to the address book – a positive signal indicating that the recipient wants your emails and wants to make sure your future messages will be delivered to the Inbox.

Message is deleted without being opened – a negative signal that your email is of no interest to the recipient.

Message is marked as spam – a very strong negative signal that your email is unwanted and is not worth to be in the Inbox.

We've been told that mailbox providers don't look at click activity when measuring engagement. If it's true, then why do many deliverability experts advise email marketers to look at click rate?

This advice primarily goes from the fact that marketers often don't have the same metrics as the mailbox providers. Most marketers can only see emails opened, read and marked as spam in their own email tracking reports. Thus, marketers are kept in the dark when it comes to other important metrics like:

  • how many of their emails were marked as "not spam";
  • how many emails were deleted without being opened;
  • how many emails were forwarded;
  • how many emails were moved to a different folder;
  • how many recipients added them to their address book.

Since these metrics aren't available to anyone, marketers and deliverability consultants have to look at the disposable data: opens, clicks, and conversions.

Following are some best practices for keeping subscribers engaged:

1. Build good relationships from the beginning. Set clear expectations, send a welcome message, and then follow with what you've promised.

2. Send engaging messages that look nicely on any device. Grab attention with compelling subject lines, content that is easy to scan and capture the essence, and offers that meet the subscribers' interests.

3. Send at the right time. Know your subscribers' audience and send messages when they're most likely to see them and take action.

4. Monitor engagement metrics. Engagement-based metrics such as "deleted unread" and "marked as not spam" provide a better way to understand Inbox filtering decisions and determine whether engagement filtering is actually a problem. These metrics are available today with data providers like Return Path.

5. Re-engage inactive subscribers. Develop a program to "wake up" inactive users and get them back. Unfortunately, every email list sooner or later will contain recipients who are not actively engaged. Re-engagement campaigns can help senders to recapture the attention of inactive recipients and not lose the list quality.

Because the recipients can become inactive for different reasons, you may need to send different re-engagement campaigns: special offers, access to exclusive content, promotion of new content, videos, tutorials or "how-to" tips, invitations to re-opt-in or opt-out, options to update email preferences or change their email address with you.

If subscribers do not respond to any re-engagement campaign, they should be removed from your mailing list to protect yourself from hard bounces, complaints, and spam traps.

4. Realtime Email Deliverability and Spam Filtering Test

Email Deliverability Best Practices

Test, test, test.

Testing email deliverability using a testing tool such as GlockApps will help you identify potential filtering issues before you send.

Within minutes, GlockApps will show you where your email is placed at different ISPs.

To generate the report, we’ll re-send your email through our personal accounts with Amazon SES, SendGrid, and Mailgun to the control list of email addresses (seed list).

But you should be aware that the deliverability may be different when you send emails through your SMTP server, delivery service or email service provider.

To test deliverability through YOUR sending infrastructure, you’ll need to create an account on GlockApps.

In your personal account, you’ll be able to create new tests and we’ll show you in real-time if there are any problems with YOUR sending system and message.

So, quick-test your email using the live test below and you’ll find the “Create My Account” button in your quick report.

We’ll show you where your email appears: Inbox or Spam

Send a copy of your email to:




Julia Gulevich is an email marketing expert and customer support professional at GlockSoft LLC with more than 15 years of experience. Author of numerous blog posts, publications, and articles about email marketing and deliverability.