What is email deliverability?

Email deliverability describes your ability to reach subscribers’ inboxes when sending emails. Strong email deliverability guarantees that your campaigns reach your customers, enabling you to achieve higher email marketing ROI.

What is a good email deliverability rate?

The ideal email deliverability rate is above 90%, with the best results closer to 99%. A sender that can achieve this inbox placement rate will also demonstrate best practices, such as a clean database, minimal spam complaints, and a low email bounce rateⓘThe percentage of emails that are undelivered vs. delivered to the intended recipient..

A deliverability rate in the 90’s range may fluctuate, but there is no cause for alarm. Some variable factors can impact your inbox placement and email delivery, including:

• Full mailboxes
• Spam filter algorithms used by different providers
• Changes to email addresses on your list
• Temporary service outages

However, if your deliverability rate continues to decline to the 80s or below, you should take immediate action. Factors such as high email bounce rates, spam complaint rates, poor list hygiene, spammy sending behaviors, or misconfigured mail servers can all affect your email deliverability.

What is the difference between email delivery and email deliverability?

Email delivery refers to the process of delivering an email to the intended recipient. As long as your email reaches the target address, it’s delivered. However, this does not indicate where the email message is, as it may land in the inbox or spam folder.

Email deliverability differs in that it refers to your ability to deliver email messages to the recipient’s inbox. For example, if you send 1,000 emails with a deliverability rate of 90%, 990 emails will reach the inbox and avoid spam.

Why email deliverability matters

Email deliverability and inbox placement rate directly impact email engagement and potential revenue. 88% of email users check their inboxes daily, with fewer likely to check spam. With more eyes on your content, you build more lasting connections that translate to sales.

Consider our case study for BarCups - a branded drinkware company.

Initially, the company used an unverified mailing list, which saw an average email engagement rate of 22%. After verifying their subscribers, they identified that 13% of the contacts were invalid or outdated. Additionally, their mail provider Mailchimp sent their infamous Omnivore warning, preventing email deliverability until the issue was remedied.

After cleaning the data and uploading the new list, the warning was removed, and email engagement rates climbed to 87%. Identifying issues that lower your reputation and email deliverability is critical for driving email revenue.

What affects email deliverability?

Before you can take steps to improve your deliverability rates, here’s a breakdown of which factors impact your email deliverability.

1. Email bounce rate

Internet and email service providers aim to protect innocent users from spammers, spoofers, and other bad actors. One way they do this is by tracking a sender’s email bounce rate.

Malicious senders aren’t interested in campaign performance. Instead, they try to reach as many people as possible, which means neglecting list hygiene and bounce rates. As your email bounce rate increases, your behavior begins to resemble that of a spammer.

The average benchmark for all industries is an email bounce rate of 2% or lower. Try to keep yours within this range, or consult your ESP for information regarding their requirements.

2. Email engagement (opens, clicks, forwards, etc.)

A subscriber that opts in to receive your emails should want to interact with them. As such, your campaign metrics, such as open and click rates, can help ISPs and ESPs understand if your list contains valid subscribers. Additionally, it can help them determine if you’re sending relevant email content to the reader.

Email engagement rates can vary by industry, but here are some average benchmarks to aim for:

• Open rate - 20%
• Click rate - 2%
• Unsubscribe rate - 0.2%

Engagement metrics may also vary depending on the types of emails you send. Use these metrics as a target goal rather than as a rule set in stone.

3. Email authenticationⓘOne or more techniques or policies created to help internet service providers determine the identity of an email sender as legitimate. Examples of email authentication include SPF, DKIM, DMARC, and BIMI. (SPF, DKIM, DMARC, BIMI)

Authenticating and securing your emails mitigates the risk of spoofing and helps you build trust with ISPs as a recognized business. Here’s a quick rundown of each:

Sender Policy Framework (SPF) – This is a list of IP addresses that you authorize to send emails using your domain.

DomainKeys Identified Mail (DKIM) – This marks the emails you send with a digital signature that ISPs use to verify each email sent from your domain.

Domain-based Messaging, Authentication, and Conformance (DMARC) – This is a framework that instructs ISPs on what to do if an email fails one or more of your email authentication checks.

Brand Indicators for Message Identification (BIMI) – This verifies you as the owner of the email with a digital certificate and brand logo.

When you implement these protocols correctly, ISPs have additional methods to verify your emails, which improves your email deliverability rate.

While SPF, DKIM, and DMARC used to be optional, major providers like Google, Yahoo, and Microsoft now require it for all senders.

4. Email content

Ensure the contents of each email are optimized before you click “send” to maximize email deliverability. Here are some guidelines to help your emails perform:

Text-to-HTML ratio – Try to keep the ratio at about 80:20. This ensures your emails remain lightweight and prevents loading or accessibility issues that can impact deliverability.

Text-to-image ratio – The accepted rule here is 60:40. Try to use images only when necessary, and use formats with smaller average file sizes like JPEG or PNG.

Email file size – The entire email, including the header, footer, body content, and attachments, should be no more than 20 MB. Consider sending files with a Google Drive or OneDrive link.

Spam trigger words – Whether certain words or phrases trigger spam filters is hotly debated. However, it’s possible that using words commonly found in obvious spam emails (e.g., giveaways, freebies, etc.) can lower your email deliverability.

See this list of spam trigger words to avoid

Failing to use best practices in any of these areas impacts the user experience. As a result, ISPs can lower your email deliverability rate if they notice an issue with your email.

5. Email sender scoreⓘOften used interchangeably with Sender Reputation. It is a score used by internet service providers to communicate your reputation with others based on your historical email-sending habits and behaviors.

Your sender score is a numerical score (0-100) that measures your sender reputation.

ISPs use the sender score to understand a sender’s historical behaviors, sending patterns, and potential threat to users. They calculate your sender score through a variety of the aforementioned factors, such as email bounce rate, spam complaint rate, sending behaviors, and email engagement rates.

Mailbox providers process billions of emails daily. By using your sender score to assess your sender reputation, they have the means to differentiate legitimate senders like you from spammers.

Email deliverability tip

Your bounce rate has a significant impact on your email score. When more than 2% of your emails bounce, your email score takes a hit. Make sure you check your contacts before you send again.

6. Your email service provider (ESP)

Your ESP also needs to maintain a positive reputation by managing the activities of every sender using the platform. Suppose ISPs notice a high influx of spammy, low-quality emails coming from a specific ESP. In that case, it can lower the email deliverability of all senders due to the poor shared IP reputationⓘA score used by internet service providers to approximate the reliability and trustworthiness of an IP address..

A quality ESP should dictate and enforce standards for all senders regarding email lists, bounce rates, spam complaints, etc. To protect its users' email deliverability, the ESP will suspend senders' accounts that don’t comply with these rules.

In addition, the ESP must use a strong infrastructure capable of processing the volume of emails sent daily by its user base. Failure to keep up with inbound and outbound requests will create deliverability issues, as more emails will bounce.

Email deliverability guidelines to reach the inbox

Next, we’ll show you how to improve email deliverability. Below, you’ll find proven rules for inbox placement along with other proven methods and tactics you can implement to maximize your deliverability rates.

Boost inbox placementⓘThe act of improving an email domain or implementing email-sending best practices in an effort to increase the probability of delivering an email message to the recipient’s inbox as opposed to the spam folder.

Reaching the inbox is critical for elevating brand visibility and generating sales. To improve your email deliverability, follow these four rules to boost inbox placement.

Rule 1 - Separate the types of emails you send

For greater control over where your emails are placed, use a dedicated IP address and email domain for each type of email (e.g., sales receipts, newsletters, etc.).

When email types mix, ISPs place your messages under “Promotions” or other tabs for safety.

To maximize your inbox placement rate:

• For corporate transactional emails – Use a domain like “your_company_name.com.”
• For other emails – Use a domain that resembles the main one. For example, a newsletter could use “your_company_name_news.com.”

Rule 2 - Use reCAPTCHA on your registration forms

You want to send emails to humans that will engage. Bot email addresses will not engage and will drag down your engagement metrics. Institute Google’s reCAPTCHA or some other human verification tool on account or newsletter signup forms to prevent bots from making it onto your mailing list.

Bots can also sign up real people. Emailing people who didn't confirm to receive emails will hurt your inbox delivery rate.

Rule 3 - Use a double opt-in confirmation for new signups

Similar to reCAPTCHA, using a double opt-in confirmation email ensures that interested subscribers are entering your mailing list.

To do this, create an automated email autoresponder that will send automatically whenever a new user submits an email signup request. The new subscriber must open the email and click on a confirmation link to reaffirm their interest in your company's marketing emails and promotions.

Doing this can mitigate bot signups and the likelihood of other visitors signing up by mistake. Keeping a list of engaged subscribers maximizes engagement opportunities and improves your email deliverability.

Rule 4 - Use a real-time email verification APIⓘAn API, or application programming interface, that allows an email verification tool to connect and communicate with another software application.

Email verification detects if an email address is valid, invalid, or some other high-risk data type.

You can install a real-time email validationⓘA process that determines if an email address uses valid syntax, exists on a given domain, and is configured to receive incoming email messages API on your website, landing pages, and anywhere else you collect new email addresses. Not only will it block fake, invalid data, but it can also alert users to typos so that they can provide their real email addresses.

A real-time email verification API keeps your list clean, reduces email bounce rates, and maximizes user engagement – all of which are necessary for boosting inbox placement and email deliverability.

Use email authentication

Email authentication protocols help build trust with ISPs, which improves email deliverability rates. ISPs can distinguish between trusted and untrustworthy senders using your domain and block or quarantine harmful emails that would otherwise jeopardize your sender reputation.

In addition, major providers like Google, Yahoo, and Microsoft now require it for better email deliverability.

Here’s how you can get started with each.

Use SPF authentication

Sender Policy Framework, or SPF, is a type of DNS record that lists all IP addresses authorized to send emails from your domain. Whenever you send an email, the receiving server compares the sending IP address to the list in the SPF record. If there is a match, the check passes, and the email is delivered.

The SPF protocol improves your email deliverability by giving ISPs a trustworthy method of verifying email ownership. Emails that pass the check are more likely to reach the inbox, while emails that fail the check bounce or go to spam.

To get started with SPF, check out these free resources:

• Guide to Mail Server Configuration – This contains instructions for implementing SPF records and other email authentication protocols with visual examples.
• SPF record generator – Use this free tool to create your SPF record automatically by providing the requested information.


Expert tip - When you first implement an SPF record, continue to allow all sent emails and pay close attention to all sending addresses. Senders may be quick to block IP addresses, inadvertently blocking legitimate senders within the company. Get to know your sending sources, and only list those IP addresses in the record.

Use DKIM authentication

DomainKeys Identified Mail, or DKIM, is a protocol for encrypting outbound emails with a digital signature. The email you send is assigned a private key, which the recipient server attempts to match with a public key found in the DKIM record. When the two match, the check passes, and the email is delivered.

Like SPF, DKIM improves email deliverability by granting ISPs a secure method of verifying email ownership. You’ll simultaneously protect your emails from spoofing by blocking sent emails that fail the DKIM check.

Here are some free resources to get started with DKIM:

• Guide to Mail Server Configuration – A comprehensive guide with instructions, examples, and screenshots on how to create and implement a DKIM record.
• DKIM record generator – Use this free tool to create your DKIM record by following the prompts.

Expert tip – While DKIM is recommended, no authentication protocol is foolproof. Consider rotating your DKIM keys as you become more familiar with the practice to ensure that they are never compromised.

Use DMARC authentication

Domain-based Messaging, Authentication, Reporting, and Conformance, or DMARC, is a protocol that contains instructions on what to do if an authentication check fails. DMARC should be used alongside SPF and DKIM records.

Whenever an email is sent, an SPF and/or DKIM check occurs if those records are present. If either of those checks fails, the ISP consults your DMARC record for further instructions. Your DMARC record will contain one of the following policies:

• None - If an authentication check fails, no action is taken.
• Quarantine - If an authentication check fails, the ISP quarantines the email by sending it to the spam folder.
• Reject - If an authentication check fails, the email is blocked.

Like SPF and DKIM, DMARC improves email deliverability by verifying you as a legitimate sender. Additionally, providers like Google, Yahoo, and Microsoft require DMARC for all mass senders.

To help you get started with DMARC, check out these resources:

• Guide to Mail Server Configuration – This guide provides instructions on how to create and implement a free DMARC DNS record using visual examples.
• ZeroBounce DMARC MonitorⓘA ZeroBounce service that helps users set up and configure DMARC, also known as Domain-Based Messaging, Authentication, and Conformance, which monitors outgoing emails and assists with email security. Users can actively monitor all outgoing emails sent from their listed domain. – This email deliverability tool walks you through creating and adding a DMARC record for your domain. It also offers 24/7 monitoring of all sent emails and automated notifications for suspicious activity.

Expert tip – If you’re new to DMARC, choose a ‘none’ policy to avoid accidentally disrupting company emails. Familiarize yourself with all senders using your domain and ensure they’re on your list of approved senders before switching to a ‘quarantine’ or ‘reject’ policy type.

DNS and CDN configuration

Next up, here are some actionable tips for improving email deliverability via speedier DNS record and content retrieval.

Use a trustworthy DNS provider

Response and loading times are key factors for improving email deliverability. It allows providers to more easily process emails for delivery, verify the sender, and point the email to its destination.

Use a DNS provider with a quality reputation. Here are some recommendations from our experts:

• DYN Managed DNS – Oracle provides both public and private DNS options with traffic load balancing and steering to optimally direct DNS requests while keeping information secure.
• Cloudflare – Used by all business types, Cloudflare offers a full suite of DNS management and optimization tools, along with reliable speed, security, and failsafe, so you’re always online.

Use a CDN for faster and secure content delivery

As mentioned above, under “What affects email deliverability,” the contents of the email are a factor. Particularly, the file size and speed at which those contents load can help you reach the inbox.

A content delivery network (CDN) speeds up processing and content delivery times by loading the content from a server that’s geographically closer to the recipient’s location. A reputable CDN can reduce file sizes via compression without quality loss, making your email more accessible.

Additionally, a quality CDN provides built-in security to protect against DDOS and other classic service attacks, which would otherwise prevent your content from loading smoothly.

Here are two CDN providers we recommend:

• Cloudflare – Cloudflare is a multi-service network for DNS records, content delivery, security, and performance. ZeroBounce is a registered partner.
• Microsoft Azure CDN – Azure CDN specializes in media streaming and file downloads for optimized delivery.

Example of a DNS record for use with CDNs

DNS Example
A Record (1.2.3.4) > "Points To " > PTR Record > "Points to" > Hostname (example.com)
(Forward)
Hostname (example.com) > "Points To" > PTR Record > "Points to" > A Record (1.2.3.4)
(Reverse)

Configure DNS PTR records for better sender reputation

Pointer, or PTR, records are a requirement alongside FCrDNS (forward-confirmed reverse DNS) records. Let’s simplify this technical jargon:

• A PTR record associates your domain name with a designated IP address. You add this PTR record to your DNS records.
• FCrDNS is an email security measure where provider spam filters look up the email domain associated with the IP address listed in the PTR record.
• The server attempts to trace the found domain name back to the listed IP address.

Not unlike email authentication, having a dedicated PTR record improves email deliverability by helping distinguish your IP address from attackers who want to hijack your email domain for phishing scams.

Here are two go-to resources to help you configure and test your PTR record:

• SPFBL – This Introduction to FCrDNS explains how to configure your mail server and check for IPv4 and IPv6 addresses.
• Mail Server Tester – After configuring your PTR record, test your configuration for free using ZeroBounce’s testing tool and correct any discovered errors.

Use email warmupⓘA service that helps email senders improve their mailing domain and IP reputation by sending genuine email content to predetermined email addresses. Users will gradually increase the volume of emails sent while receiving positive engagement through an automated process. tools

Warming up an email IP address is critical. Gradually introducing your emails to a new IP allows your company to establish its sender reputation. Once you have a foothold, you can reap the benefits of your email marketing efforts.

However, don’t send too many emails at once. If your sending platform supports the feature, set limits per hour or day for each of the IPs per email domain. If you send too many emails early on, you’re more likely to see your bounce rate increase.

Here are the suggested limits per provider that you should follow in your first 30 days of mailing:

Suggested rate limits for email service providers

200 emails/day/IP (for at least five days, then you can double-up every day)

200 emails/day//IP (for at least five days, then you can double-up every day)

200 emails/day/IP (for at least five days, then you can double-up every day)

200 emails/day//IP (for at least five days, then you can double-up every day)

50 emails/day/IP

100 emails/hour/IP

100 emails/connection/IP (up to 5 IPs)

Zero Bounce

You should also always visit the postmaster website of the domains you’re trying to send to in bulk. You’ll often find the sending limits published within their bulk sender guidelines.

Here are some example strategies for email warmup:

• Start a new warmup for the existing IP
• Send only to subscribers who have opened at least one email in the last 30 days
• Limit your starting volume to 3,000 subscribers
• Keep sending to those subscribers only for the first three days before increasing the volume
• Increase the volume by 1,500 subscribers with opens in the last 30 days. Your new total volume should be 4,500 subscribers
• Keep sending to the new volume of 4,500 for two more days
• Follow this strategy to increase the volume every two or three days by 50% of the actual volume
• After ten days, you can start increasing the volume by doubling it

Check for spam trigger words

Even after implementing the above tactics, spammy content within the email can trigger spam filters. Though the relevance of spam trigger words is debated, it’s a recommended practice to avoid using scam-like words, such as:

• Eliminate debt
• Credit card
• Act fast
• Click this link

Check your subject lines and body content using this free spam analyzer:

Check this list of 117 spam trigger words

Check your feedback loops (FBL)

Feedback loops, also called complaint feedback loops, alerts senders to spam complaints. When a recipient marks an email as spam, your ISP notifies you so that you can unsubscribe and remove the reader from your mailing list.

Keeping your spam complaint rate below the 0.1% benchmark is critical for maintaining strong email deliverability rates. Make use of one of these FBLs:

• Yahoo! Sender Hub – Enroll in an FBL with a free Yahoo! Account. This service includes additional tools, such as schema and BIMI, to enhance email deliverability.
• Comcast FBL - This is recommended for businesses sending high email volumes to Comcast addresses.
• Gmail FBL - Here are Google’s official guidelines for implementing an FBL. Note that Gmail’s FBL is only available for ESPs who are MAAWG members (Messaging, Malware, and Mobile Anti-Abuse Group).
• Zoho FBL – If you use Zoho for email delivery or send emails to Zoho addresses, this FBL service is ideal for improving email deliverability.

Monitoring your IP and domain health

After implementing the essential email deliverability tactics mentioned above, monitoring your IP and domain health is critical. Keeping tabs on both helps you identify and resolve common email issues such as blacklisting, bounce rates, and other facts that can create a poor sender reputation.

Check out these free tools for domain monitoring:

• Google Postmaster – Track IP and domain reputation, FBLs, authentication compliance, encryption rates, spam rates, and other delivery errors.
• Hotmail/Outlook Smart Network Data Service – Get assistance with monitoring IP reputation, complaints per IP, traps per IP, and Ehlo/Helo commands.

Monitor email blacklists for better deliverability

Service providers use email blacklists to keep a record of untrustworthy email domains and IP addresses. If your domain or IP is blacklisted, it will drastically reduce your email deliverability rates as your emails are automatically blocked.

However, you can stay on top of this issue via blacklist monitoringⓘA service that actively observes your email domain and IP address while comparing it to known email blacklists and antispam services around the internet. If a blacklist flags either the domain or IP, the monitor will notify the user.. By registering your domain and IP with a monitor, you’ll automatically be notified when and where a blacklisting occurs. You can then take action to remedy the issue before it can further impact your email deliverability.

Here are our recommended blacklist monitoring tools:

• ZeroBounce Blacklist Monitor – You can monitor your domain and/or IP address for free against 200+ known blacklist providers. Get automated alerts whenever an issue occurs.
• BarracudaCentral – Look up your IP or domain reputation and submit removal requests.

Email whitelists can guarantee email deliverability

A whitelist is the opposite of a blacklist and is a list of pre-approved IP addresses or domains. Whitelisting your domain can grant improved email deliverability rates due to less restrictive spam filtering and allowance for increased sending volumes.

Note that it’s recommended to wait at least 90 days after your first email, as whitelisting services need to review your sending history before you can use one.

Here are some recommended whitelisting services:

• United Online – This is a free postmaster tool for whitelisting your business email domain.
• Certified Senders Alliance (CSA) – A paid service that can certify your business domain as a trustworthy, reputable sender for whitelisting.

Improve your email list quality

The quality of your email list is critical for improving email deliverability. If your list contains invalid or fake data, your email bounce rate will increase significantly. Additionally, invalid or inactive subscribers lower your email engagement metrics, which can also decrease deliverability rates.

Here’s what to do to improve your list quality.

Email deliverability tip

Email list quality significantly impacts email sender score. If your sender score is less than 90, take action ASAP to improve it.

Industry best practices for high email deliverability

Here are 13 best practices used by top email marketers and senders that help guarantee maximum email deliverability rates.

Don’t use too many connections per IP

Every ISP limits the number of connections allowed per IP address. The table below shows each ISP’s rate limits.

Email privacy laws and compliance

Honor all unsubscribe requests (CAN-SPAM)

You can’t keep subscribers on your email list against their will. Plus, it’s a terrible way to boost your email deliverability.

When a reader asks to unsubscribe - whether through an unsubscribe link or manually - honor their request promptly. CAN-SPAM law specifies that you only have ten days to do this.

Email deliverability tip

When you comply with email law, everything becomes easier for you to whitelist and improve your email deliverability.

Comply with all privacy laws

It’s critical to stay up-to-date with the latest privacy laws in email. Be sure to comply with CASL and CCPA for CA, CAN-SPAM in the United States, DPEC, and GDPR for the European Union.

When you adhere to the law, everything becomes easier to whitelist, and managing your reputation is obstacle-free.

Here are resources to learn more about significant email privacy laws:

• CAN-SPAM (US)
• CASL (CA)
• DPEC (EU)
• GDPR (EU)
• Digital Personal Data Protection (IN)
• HIPAA (US)

Establishing MX records

A mail exchanger (MX) record dictates which email server should accept incoming email messages on behalf of the destination domain. RFC standards state that if an MX record is missing, the A record should be used as the mail server.

• MX record - Mail exchanger record; specifies which email server should accept email on behalf of the domain
• A record - A record that determines which IP address hosts the email domain

However, many ISPs don’t follow this standard, making an MX record necessary for successful email delivery.

Be sure to test new MX records, as different ISPs use different spam filters. What Yahoo places in the inbox, Gmail may relegate to spam. Use an inbox placement tester to avoid email deliverability issues.