Improve email deliverability: 50+ proven steps from experts

Email delivery and sender reputation are crucial to a successful transactional or marketing email campaign. Read our checklist to find out more. 

Email Deliverability Expert

Abhinav Meethale Parambath

Email Deliverability Expert

Are your emails not reaching your audience? Is your brand’s reputation suffering because of low email deliverability? In today’s fast-paced digital world, where communication happens at the click of a button, it’s crucial to ensure that your emails make it to the intended recipients.  

Imagine this: you’ve spent hours crafting the perfect email campaign, meticulously selecting the right words, designing eye-catching visuals, and including irresistible offers and critical information. You hit that send button, eagerly waiting for responses and conversions. However, instead your inbox remains eerily silent, and your delivery reports paint a disappointing picture of undelivered emails. 

Low email deliverability not only hampers your brand’s reputation but also affects customer experience and engagement. When your emails don’t reach the intended recipients, you miss out on valuable opportunities to connect, sell, and interact with your audience. It’s like hosting a party but forgetting to send out the invitations. No guests, no fun, and no return on investment. 

Drawing from our vast experience, we have compiled a step-by-step checklist that will empower you to improve the deliverability of your email campaigns. Whether you’re sending transactional emails or running large-scale promotional campaigns, our guide has got you covered.  

We’ve broken down the auditing process into three key phases with a checklist for each:  

  • Email setup 
  • Onboarding 
  • Execution 

We discuss what you need to optimize your email deliverability, build a solid sender reputation and craft effective domain and IP strategies. 

Email setup

When setting up your email account there are three crucial points you need to consider: 

  • Selecting the right email service provider 
  • Your domain strategy 
  • The type of IP address 
  • Authenticating the domain 

Selecting the right email service provider

Choosing the right email service provider (ESP) is a critical decision and long-term commitment. To zero in on the right ESP, follow the below checklist:

  • Test ESP performance: Put the ESP to the test with trial periods or pilot projects. Check for high deliverability rates (95-98%), fast delivery, user-friendly interface, easy integration, and robust reporting. 
  • Consider pricing plans: Review pricing structures and choose an ESP that fits your budget. Look for volume-based pricing options for high email volume to align costs with consumption. 
  • Evaluate deliverability support: Ensure the ESP offers excellent customer support and a dedicated email deliverability team. They should help troubleshoot, provide best practices, and maintain high inbox placement and sender reputation.  
  • Migrate email content and data: Transfer all email content, including templates and images, to the new ESP. Import bounce, complaint, and unsubscribe data as suppressed data to avoid emailing unsubscribed customers and protect your reputation. 

Why choose Infobip’s Email API as your ESP


capacity of emails per minute

2 sec

average delivery time


deliverability rate achieved

Domain strategy

Now that you’ve found the right ESP, it’s time to have a look at your domain strategy. Domain strategy directly impacts the sender’s reputation and increases the chances of emails reaching the recipients’ inbox instead of their spam folder. 

  • Avoid corporate domains for bulk campaigns: Protect your sender’s reputation by using subdomains instead of your brand’s main domain for bulk emailing.  
  • Use different subdomains for different sending purposes: Maintain separate reputations by using different subdomains for various types of emails. This ensures that issues with one type of email won’t affect the deliverability of others. However, it is acceptable to use different local parts of the sender address for smaller volumes of emails. *See table below.
  • Say no to cousin domains: Steer clear of cousin domains that deviate from your brand’s main domain. Stick to your brand identity and maintain consistency. 
  • Utilize “send behalf of” feature: If you must use the corporate domain as the “from-address,” use the “send behalf of” feature to send emails from a subdomain while displaying the corporate domain as the sender.
  • Avoid brand-new domains as “from-address”: New domains lack a reputation with inbox providers, leading to potential deliverability issues. Choose domains with an established email sending history to increase deliverability and minimize spam filtering. 
  • Skip the “no-reply” address: Don’t trigger spam filters and reduce customer interactions by using “no-reply” as the local part of the sender’s email address. Opt for recognizable and readable addresses that encourage engagement. 
  • Don’t use parked domains as sender domains: Avoid using domains that are registered but not connected to any online service. Choose active and relevant domains to enhance your email campaigns’ effectiveness. 
Type of email trafficExample of subdomain
Use different subdomains for different sending purposes

IP strategy

Next step is choosing your IP strategy. There are two types of IPs used in email marketing to choose from, and we list out the pros and cons of both.

Dedicated IPs

IP reputation is determined solely by your behaviour

Better control over email deliverability

Ensure faster email delivery
Need to maintain a minimum sending volume and frequency

Need IP warm-up for 6-8 weeks based on volume

Usually more expensive

Business criteria:

  • Send frequently, more than 3 times per week. If you stop sending emails for a few weeks, the ISP will treat you as a new sender, requiring domain warming. 
  • Send a minimum of 100,000 emails per month. A certain amount of sending is necessary to establish a solid reputation, low-sending volumes may be suspicious and treated as spam.
  • Timely delivery is crucial for you. Example, for transactional emails a blocklisted shared IP won’t affect delivery time.
  • You have time to warm-up dedicated IPs.
  • You are ready to pay for dedicated IPs.

Shared IPs

A low level of sending volume is acceptable

Already warmed up and quicker time to market

Cheaper in cost
IP reputation depends on all users’ behaviour

Less control over deliverability

Can affect timely delivery of emails

Business criteria:

  • Send occasional campaigns.
  • Send less than 100,000 emails per month.
  • No need to send time-critical emails.
  • Need to get up and running quickly with no time for warm up.
  • Have budget constraints.

Boost deliverability with multiple dedicated IPs

Gain greater control over deliverability by using different dedicated IPs for different purposes. For instance, send transactional emails from IP #1 and promotional emails from IP #2. While there isn’t a strict limit, it’s not advisable to send over 2 million emails per day from a single dedicated IP.  

Domain authentication

The next step is to verify the legitimacy of your email sender ID and confirm you have the authority to use a specific domain name in the email address. This helps prevent email fraud, such as phishing scams and other types of email-based attacks. 

Checklist for domain authentication:

Implement DNS and authentication records during domain registration: 

Verify all records using verification tools: 

  • Thoroughly verify records using reliable tools like Mr. Toolbox to identify and fix any issues promptly. 

Test configuration and deliverability with email testing tools: 

  • Use tools like Mail-Tester to test your configuration and check deliverability scores. 
  • Contact your ESP support if any issues arise for resolution. 

Register your domain in Google Postmaster Tools: 

  • Sign up for Google Postmaster Tools to monitor and optimize email delivery to Gmail users. 
  • Track domain reputation, spam rate, and email authentication to improve deliverability. 
  • Follow the setup steps on the official Google page or seek assistance from your ESP support. 

By following this checklist, you’ll ensure proper domain authentication, enhance email deliverability, and optimize your communication with recipients. 


Domain warmup is crucial for ensuring email deliverability by gradually establishing a positive sending history and building trust with inbox providers, preventing emails from being marked as spam. 

Domain warmup checklist:

Follow warm-up plan and increase volume gradually:

  • Implement a warmup plan and start with a small volume
  • Gradually increase the number of emails sent over time
  • This builds trust and avoids spam filters

Target highly active list first:

  • Prioritize subscribers who recently engaged with emails or your product. 
  • Focus on establishing positive engagement signals. 
  • ISPs perceive active senders with valuable content as reliable. 

Use a mixed ISP list for email traffic distribution:

  • Include subscribers from various ISPs (Gmail, Outlook, etc.). 
  • Diversify your recipient base to enhance deliverability. 
  • Building a positive reputation across multiple providers improves overall deliverability. 

Maintain consistency in sending pattern: 

  • Be consistent with volume, frequency, and content. 
  • Establish a predictable pattern for ISPs and mailbox providers. 
  • Build trust and credibility by avoiding sudden spikes or lulls in sending activity. 

Use throttling techniquest to Increase volume-based on performance metrics: 

  • Analyze open rates, click-through rates, and spam complaints. 
  • Incrementally increase email volume based on positive performance indicators. 
  • Scale up email marketing efforts effectively without negative consequences. 

By following this checklist, you’ll successfully warm up your email marketing account, improve deliverability, and establish a positive reputation with inbox providers. 

Why is domain warm up important? 

A global ride-sharing company faced poor deliverability of emails on their Microsoft domain, which effected over 550 million email recipients. The main challenge was not having the throttling capability to stagger email deployments over time to limit the volume of emails being sent to recipients which resulted in the ride-sharing app having to redo the domain warmup. 

This caused undelivered emails, downtime and loss of time and resources.  

To resolve the issue, the Infobip team used our Email API warmup feature to onboard each of the 20 IP addresses used by the ride-sharing app in a time-efficient manner. Then the team divided the emails sent by IP, thereby, limiting the volume and ensuring speedy delivery. 

Email execution  

During the Execution phase of email campaigns, recipient list management, content optimization, and delivery monitoring take center stage as crucial elements to ensure optimal deliverability and engagement. 

Recipient list management 

Recipient list management is a crucial aspect of email marketing that involves maintaining a clean, engaged, and targeted audience to maximize deliverability and campaign performance. A well-managed list with a low bounce rate, low complaint rate, and high engagement signals to ISPs that you are a legitimate sender with quality content, so your chances of reaching inboxes are higher. 

Here is an eight-step checklist to manage your email recipient list: 

  1. Don’t buy email contact lists: Instead, focus on organic list building strategies to cultivate a qualified and engaged audience. 
  2. Use a double opt-in rather than single opt-in process: Implement a confirmation process to verify email addresses and reduce spam complaints. 
  3. Regularly use email validation tools to clean mailing lists: Identify and remove invalid or risky email addresses from your list. 
  4. Remove non-engaged/ inactive subscribers from the lists: Keep your list healthy by removing subscribers who haven’t shown activity or engagement. 
  5. Make unsubscribe process simple: Provide an easy and accessible unsubscribe option to respect subscriber preferences. 
  6. Segment email list based on subscriber behavior and interests: Deliver targeted and personalized content by dividing your list into distinct segments.
  7. Allow subscribers to share their preferences: Involve subscribers in sharing their content preferences and email frequency.
  8. Suppress bounces and spam complaints: Monitor bounce notifications, handle spam complaints promptly, and maintain a positive sender reputation. 

Content optimization 

Content optimization is crucial for improving email deliverability and avoiding spam filters. Here’s a 13-point checklist to help you optimize your email content: 

  1. Use clear and compelling subject lines. 
  2. Avoid spam-triggering words and phrases. 
  3. Provide relevant, valuable, and personalized content. 
  4. Craft clear call-to-action (CTA) statements. 
  5. Include an unsubscribe option. 
  6. Use concise and scannable content format. 
  7. Ensure mobile optimization. 
  8. Avoid using too many images. 
  9. Use consistent design elements. 
  10. Avoid URL shorteners. 
  11. Optimize HTML and text versions. 
  12. Test and proofread your emails. 
  13. Comply with legal requirements. 

Deliverability monitoring 

Analyzing key metrics and monitoring your reputation is crucial to understand existing issues and make improvements. Below is the checklist of metrics you should monitor. 

Keep on eye/track essential metrics:

  • Delivery rate: Infobip’s standard is 97%-99% 
  • Bounce rate: ideally between or less than 2-3%   
  • Open rate: from 15% to 25% for marketing emails, and 40-65% for transactional  
  • Click-through rate (CTR): ideally between 2% and 5% 
  • Click-to-open rate (CTOR): typically, between or greater than 20-30% 
  • Unsubscribe rate: ideally below 1% 
  • Spam complaints: ideally less than 0.2%. 

Engagement metrics like clicks, opens, and CTOR (Click-to-Open Rate) impact sender reputation and email deliverability. High engagement indicates value to subscribers and improves inbox placement, while sudden fluctuations in these metrics can indicate reputation issues that need resolution with your ESP. 

Check Google Postmaster and monitor reports daily:

Google Postmaster Tools is a free service provided by Google that helps email senders and administrators monitor and improve their email deliverability to Gmail users. The service provides valuable insights about deliverability and includes reports about: 

1. IP Reputation: Shows how Gmail’s spam filters view your IP address and domain reputation. 

2. Authentication: Indicates if you have properly set up SPF, DKIM, and DMARC for email authentication to stop spammers and phishers from using a domain they don’t have a right to. 

3. Encryption: Shows whether the sender has properly configured Transport Layer Security (TLS) encryption to protect email in transit 

4. Delivery Errors: Highlights any errors encountered in delivering your email messages 

Monitor SNDS reports with your ESP: 

SNDS (Smart Network Data Services) is a free reporting tool provided by Microsoft that helps monitor email senders and improve their email deliverability to Outlook and other Microsoft email services. Request your ESP`s expertise to provide you with valuable insights and metrics on email delivery, including: 

  • Complaints: show how many users have marked the sender’s emails as spam or junk. 
  • Spam trap hits: shows whether the sender has sent emails to inactive email addresses or known spam traps. 
  • Volume: shows the number of emails sent to Microsoft email services. 
  • Sender reputation: shows how Microsoft’s spam filters view the sender’s IP address and domain reputation. 

Check whether your IP/domain is blocklisted:

Regularly check if your domain or IP address has been blocked. Utilize reputable online blocklist checking services to ensure your emails are not being flagged as spam. If you are listed somewhere, try to get delisted. Some sites where you can check this are: 

Monitor inbox placement:

Use the following tool to check if emails are in the Inbox or spam folder. 

Check your sender score:

Check your sender score to monitor your domain and email reputation via Send Score to check you sender reputation. Sender score is calculated on a scale of one to  hundred which is the optimal score. 

Resolving deliverability issues use case 


A fintech company with a database of 4 million users faced issues with throttling and bounces specifically from Gmail. The problems arose due to a failure to follow the warm-up plan, high rates of hard bounces, and sudden spikes in volume.


After careful analysis by Infobip’s Email API team, it was identified that the initial operations started with high volumes without proper warm-up, resulting in poor data quality and increased hard bounces. Additionally, abrupt surges in traffic from new domains and IPs led to throttling and subsequent soft bounces. The content utilized lacked effectiveness due to the absence of clear call-to-action (CTA) and non-compliance with email best practices and mobile-friendly design, all of which negatively impacted the sender’s reputation.


To address these issues, the Infobip team setup auto alerts to notify clients and our team about high hard bounce rates, prompting a temporary pause in sending to prevent further damage. List validation services were recommended to ensure data quality, and sending high volumes was put on hold until the validation process was completed. A customized warm-up plan was developed, focusing on targeting recent engagers and double opt-in users. To scale the volume, four new domains were added. Guidance on email best practices and content optimization was provided to optimize deliverability


The results were significant. The implementation of email validation reduced hard bounces, while diligently following the warm-up plan resolved soft bounces and improved delivery rates. With the successful resolution of delivery issues, the client was advised to gradually increase the volume of their email campaigns. 

In conclusion, maintaining good email deliverability is crucial for the success of your email campaigns. By adhering to our checklist of best practices and implementing strategies such as managing your email list, using a reputable email service provider, personalizing content, and avoiding spam trigger words, you can boost your email deliverability rates and ensure that your messages reach the inboxes of your subscribers.  

Improve your email delivery and sender reputation with Email API

Jun 28th, 2023
2 min read
Email Deliverability Expert

Abhinav Meethale Parambath

Email Deliverability Expert