The pro's checklist to email deliverability

By Nayana Somaratna

Last updated: April 16th, 2020

If you’re reading this, then you probably have some experience with email deliverability in your day-to-day work. In fact, there’s a good chance that you have a sound list of dos and don’ts in place already.

We’d like to share with you our own 44 point checklist, which we’ve put together after years of experience with this stuff. Our checklist is comprehensive and may likely overlap with many of your own best practices. However, we believe that you’ll find here fresh new insights (including all our reasoning behind each point) - knowledge you can truly capitalize on.

With that said, let’s jump into our pro’s checklist!

The checklist categories

Since 44 points may seem like a lot, we’ll start with organizing them into clear email component categories:

Subscribers list
Authentication infrastructure
Sending infrastructure
Content personalization
Content quality
Content call-to-action (engagement)

These categories have no particular order and can be scrutinized independently. At the end of our article, we’ll provide you with a checklist summarizing the items explored.

OK, let’s dig deeper into each category’s suggested action items and the rationale behind them.

Subscribers list

Action item(s) for usability
  1. Double opt-in all new subscribers
  2. Re-permission existing subscribers who were single opt-in

Make sure all your subscribers have consented to receiving your emails. If more than a few subscribers manually mark your emails as spam, their email service provider will assume you’re sending spam.

Action item(s) for maintenance
  1. Remove hard bounced email addresses
  2. Remove soft bounced email addresses with more than 3 soft bounces

Avoid sending emails to invalid or non-existent email addresses. If too many of your emails bounce, email service providers may assume you’re sending emails indiscriminately.

Action item(s) for continuous growth
  1. Remove subscribers with no engagements for more than 3 months

If a subscriber has not opened any of your emails for 3 months or more, remove the subscriber from your subscribers list. The lower the percentage of subscribers who open your emails, the higher the likelihood their email service provider will assume that you’re sending spam. Also, certain email addresses can become “spam traps”: a practice where email service providers keep open email accounts already closed by users in order to trap would-be spammers. Emailing such an address is a guarantee that you’ll be marked as a spammer.

Authentication infrastructure

Action item(s) for tech setup
  1. Implement Sender Policy Framework (SPF)
  2. Implement DomainKeys Identified Mail (DKIM)
  3. Implement Domain-based Message Authentication, Reporting & Conformance (DMARC)
  4. Implement reverse DNS

Ensure that these technical parameters have been set up properly. Most email delivery services (e.g., SendGrid, Mailgun, etc.) do this automatically for you. If SPF and DKIM haven’t been implemented, your emails will most likely end up in the spam folder. DMARC and reverse DNS are less important, but should be set up if possible.

Action item(s) for domain ownership
  1. Use a custom domain

Send emails from your own domain (e.g., Avoid using a public service (e.g.,, etc.). Using a custom domain increases your credibility. This also allows you to control your sender reputation.

Action item(s) for domain nomenclature
  1. Avoid unusual characters in domain name

Avoid special characters in your custom domain names, especially homographs. Many phishing emails use special characters to fool readers (such as typing something that seems legitimate, ɢ; but with a unicode character that isn’t authentic, ɢ). Using similar characters in your domain name increases the likelihood of your emails being marked as spam.

Sending infrastructure

Action item(s) for single IP/email addresses
  1. If using a single IP address, try to use the same IP address

If you’re using an email delivery service that supports dedicated IP addresses, or if you are running your own dedicated email infrastructure, make sure to use the same IP address all the time. Sender reputation is specific to a given sender email address and IP address. For more details, please read the item Check sender reputation of email domain.

Action item(s) for multiple IP/email addresses
  1. If using multiple IP addresses, use a separate IP address for each message type
  2. Use different sender email addresses for different message types
  3. Always use the same sender email address for the same message type

When sending different types of messages (e.g., promotional messages, customer support messages, etc.) use a different sender email address (e.g.,, If possible, use a separate dedicated IP address for each message type as well. Different types of messages will have different open rates. For example, transactional emails (e.g., confirm email address, reset password, etc.) have higher open rates than marketing emails. Separating message types ensures that crucial transactional emails are less likely to end up in spam. Please also see the item Avoid having multiple message types in the same email.

Action item(s) for new IP/email addresses
  1. If using a new dedicated IP address, send emails at low volumes initially and scale volume over time
  2. If using a new sender email address, send emails at low volume initially and scale volume over time

Email service providers are very careful with new sender email addresses and dedicated IP addresses. If you start sending large volumes of email at once, you may be flagged as a spammer.

Action item(s) for seed lists
  1. Test emails against seed list before sending

Before sending your emails to your entire list of subscribers, send them to a small number of real email addresses. This helps detect deliverability issues prior to committing yourself and wasting valuable opportunities resulting from a positive first impression with subscribers.


Action item(s) for domain safety/security
  1. Check if email domain is listed as unsafe or insecure
  2. Check if dedicated IP address is blacklisted
  3. Check if email domain is blacklisted

Check if your domain name is already blacklisted or marked as unsafe or insecure. If you’re using your own email sending infrastructure, do the same for any dedicated IP addresses you have. If any of these have been marked as unsafe or blacklisted, your emails will end up in spam. In such a scenario, you may wish to consider obtaining a new domain name or IP address.

Action item(s) for sender reputation
  1. Check sender reputation of dedicated IP address
  2. Check sender reputation of email domain

Conventional wisdom recommends that you check your “sender reputation” to see if your domain or IP address has a low reputation. The lower the reputation, the more likely your emails are to end up in spam. Your sender reputation is a score calculated by email service providers. Based on your score, email service providers classify you as either a good, neutral, or bad sender. The worse your reputation is, the more likely it is that your emails will end up in spam.

The reputation of a sender and the algorithms used to calculate the sender’s scores are unique to each email service provider, and are well-kept secrets. There’s no way for you (or anyone else, really) to know what your actual sender reputation might be. Nevertheless, several 3rd parties attempt to guess your “sender reputation” using their own proprietary algorithms. In our company, we don’t use any algorithms (proprietary or from a 3rd party). But since the use of algorithms is common industry practice, we’ve included the item in our checklist.

Action item(s) for feedback loops
  1. Check feedback loops of major email service providers

If you’re sending a large number of emails, make use of the “feedback loops” offered by the major email service providers. If you’re emailing Gmail or G-Suite addresses, use Google’s Postmaster Tools. Feedback loops will help you identify which emails or campaigns are going into spam.

Content personalization

Action item(s) for subscriber segments
  1. Segment your subscribers by type

Divide your subscribers into “segments” based on their profiles and interests (e.g., customers, partners, etc.). Customizing your emails by segment leads to better open rates and a lower risk of subscribers manually tagging your emails as spam. Over time, this will result in lower automated spam rates for you as well.

Action item(s) for segment messaging
  1. Send each segment only appropriate messages

Send only appropriate messages to each subscriber segment. Sending only appropriate messages to each separate segment will lead to better open rates and a lower risk of subscribers manually tagging your emails as spam. Over time, this too will result in lower automated spam rates for you as well.

Action item(s) for message personalization
  1. Personalize email by subscriber

At a minimum, personalize each email by including the subscriber’s name. The more personalized and customized the emails you send, the better. Including the subscriber’s name in the email subject or body signifies that you know who they are. This reduces the likelihood of your email being spammed.

Content quality

Action item(s) for tracking elements
  1. Use at most 1 tracking pixel

Certain tools (e.g., customer relationship management software, mailing list software, etc.) embed a tracking pixel in your emails. Tracking pixels are tiny images that are loaded from a URL when a user opens that email. A unique tracking pixel is generated for each subscriber, therefore allowing senders to track if and when the emails sent are opened. If you’re using several such tools at once, your emails may contain multiple tracking pixels. The higher the number of tracking pixels, the greater the chance that your emails will be marked as spam.

Action item(s) for external images
  1. Avoid external images

Ensure that all images are embedded into the emails themselves. Avoid images that are loaded from a URL. This is because external images can be used to track email opens, similar to tracking pixels. Therefore, email service providers treat them similarly, and may mark your emails as spam.

Action item(s) for shortened links
  1. Avoid shortened links

Avoid using links that have been run through a link shortener (e.g.,,,, etc.). Short links obfuscate the destination domain, so they’re often used in phishing attempts. Using them may lead email service providers to mark your emails as spam.

Action item(s) for trigger words
  1. Avoid spam filter trigger words in subject
  2. Avoid spam filter trigger words in body

Certain words and phrases are common in spam and phishing emails. Avoid using them if possible.

Action item(s) for HTML quality
  1. Avoid malformed HTML

If your emails have an HTML body, make sure the HTML is properly formed. Most email composition interfaces (e.g., Gmail’s send new email popup) do this for you automatically. Email service providers may mark emails with malformed HTML as spam, due to the following reasons:

Action item(s) for hidden content
  1. Avoid hiding content

Avoid using HTML/CSS tricks to hide content. Many phishing emails use this tactic to hide links and dangerous content. If you do so, your emails may also end up in the spam folder.

Action item(s) for text formatting
  1. Avoid unusual formatting

Minimize the use of multiple colors. Avoid using all caps (e.g., “HELLO, HOW ARE YOU?”) or similar non-standard writing styles. Many spam emails have unusual text formatting and unnatural writing styles. These enhancements simply increase the risk of email service providers sending your emails to spam.

Action item(s) for images
  1. Ensure that images comprise less than 40% of the content

Conventional wisdom suggests that emails that are mostly composed of images are more likely be sent to spam. Our team is currently testing this hypothesis. So, for now, we’ve decided to keep it in the checklist until we have enough data to argue otherwise.

Action item(s) for ALT text
  1. Include alternative (ALT) text for embedded images

If your emails have important images, make sure to add specific ALT text that will be displayed should recipients disable disable image loading. Certain subscribers (especially if they’re tech-savvy) will disable the display of images inside emails. Including ALT text ensures that the emails are readable nonetheless. Email service providers may consider the lack of ALT text another reason your emails must go into spam.

Action item(s) for text length
  1. Keep your email short

Keep your emails short and to the point. Short and focused emails have better delivery rates.

Action item(s) for message objectives
  1. Avoid having multiple message objectives in the same email

Avoid multiple communication objectives in a same email (e.g., do not add a product promotion message to a confirm your email address email). Including multiple objectives in a same email increases the likelihood that it will end up in spam.

Action item(s) for signatures
  1. Ensure that the name in the signature and sender name match

If your emails have a signature, make sure the name of the sender and name in the signature match. Email service providers may consider a mismatch to indicate that your email is spam or a phishing attempt.


Action item(s) for subscriber requests
  1. Ask subscribers to move emails from spam or promo folder to inbox
  2. Ask subscribers to add the sender email address to the contacts list

Ask your subscribers to manually move your emails from the spam folder to the inbox. Just as subscribers manually spamming your emails is a strong signal to email service providers that you are sending spam, their doing the opposite is a strong signal that you are not sending spam. The more users that do this, the better for you.

Just the same, ask your subscribers to add your sender email address or addresses to their contacts list. Emails coming from email addresses in a recipient’s contact list are less likely to end up in spam.

Action item(s) for unsubscribe links
  1. Include unsubscribe link in email
  2. Include one-click unsubscribe link or header parameter

Make sure that your emails have an unsubscribe link. Most email delivery services (e.g., SendGrid, Mailgun, etc.) do this automatically for you. If you don’t provide an unsubscribe link, email service providers are more likely to mark your email as spam. Moreover, if you don’t provide a clear unsubscribe option, users who do not wish to continue receiving your emails will be forced to manually spam your emails. This may severely impact your deliverability.

Just the same, include a one-click unsubscribe option in your emails. Many email delivery services (e.g., SendGrid, Mailgun, etc.) do this automatically for you. If your email has a one-click unsubscribe option, if a subscriber decides to mark your email as spam, the email service provider will display them a popup asking if they wish to unsubscribe instead. This will help avoid the deleterious effect of your emails being manually spammed.

Please also see the item Double opt-in all new subscribers.

In summary

Now that we’ve gone over all 44 points in our checklist, here you have them for your personal use:

As to us, we’re Monsoon Yeti, an education based marketing team to help you engage audiences better. For this specific topic of email deliverability, we offer our own email vetting tool, which allows you to safely determine whether an email subject line and body you’re about to send will be marked as spam by your audiences’ email service providers (i.e., "Inbox Placement").

Vetter is one of several other tools we offer at Monsoon Yeti, all related to education based marketing. If you require additional information or support, reach out to us at:

Try Vetter today

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