16 Email Deliverability Best Practices To Boost Deliverability Rates

Struggling with low email deliverability? In this blog, we’ll share the best practices to help you boost your email deliverability rates and connect with more of your audience.

Table of contents

• What is Email Deliverability?
• 16 Email Deliverability Best Practices To Boost Deliverability Rates
• What Affects Email Deliverability Rate?
• Why Deliverability Matters in Email Outreach
• How Allegrow Enhances Email Deliverability for Sales and Marketing Teams

What is Email Deliverability?

Email deliverability, simply put, is the ability to deliver emails to a user's inbox, as opposed to an email ending up in the spam folder. 

The likelihood of whether your emails reach your users depends on how well you handle certain factors, including:

• Technical setup to meet email service providers (ESPs) authentication requirements
• Throttling and domain warm-up
• Bounces 
• Being flagged as spam–by the end user or the ESP
• Bulk sending; frequency and volume
• The IP and domain you’re sending from

Additionally, engagement is a key driver of whether the above factors have positive or negative results, and some elements can impact engagement with your emails and therefore hurt deliverability. To name a few:

• Making it difficult to unsubscribe
• Use of links and attachments
• Opt-ins and follow-ups
• Email content and subject lines

Let’s dive into some of the core areas that you should focus on.

Understanding Email Bounces: Types, Causes, and How to Track Delivery Rates

Typically, there are two common causes for emails bouncing. One usually has something to do with the recipient's email address. The user may have changed jobs, or the email was generated incorrectly in the first place. 

The other has to do with the email being rejected by the recipient's email service providers (ESP), this may be due to technical setup, or a whole host of reasons.

ESPs offer insights as to why a message was rejected (bounced) based on the details the receiving server sends back in the error message, for example, 550 5.4.1 recipient address rejected. You can see a list of the most common bounce codes here. 

Having a high bounce rate is an indicator that your emails are being flagged as spam by ESPs. Measuring bounce rate will serve as an indicator that your emails are being delivered, with the industry average sitting at 0.41%. 

The Role of Sender Reputation in Achieving Optimal Email Deliverability Rates

Sender reputation is like your email's credit score. When it’s high, you can expect your emails to land in the primary inbox and receive engagement, and when it’s low, even important emails like calendar invites or proposals can get lost.

When you focus on creating emails that connect with your audience, you’re not just keeping them interested; you’re also building a solid sender reputation. This helps ensure your emails land in inboxes instead of spam folders.

Engagement is the most critical factor in deliverability since it directly impacts the sender’s reputation (both for the marketer and the ESP). A stellar sender reputation is key to excellent email deliverability, and mailboxes should have a sender reputation of over 90 as a minimum score to ensure emails land in the reader’s inbox.

 So, when you prioritize engagement, you’re actually giving your sender reputation a boost, which leads to better response rates, more clicks, and ultimately, more conversions. 

Related Reading

• The Definitive Guide To Email Deliverability

16 Email Deliverability Best Practices To Boost Deliverability Rates

1. Authenticate Your Emails 

Proper email authentication is essential to verify that your messages are legitimate and sent from a trusted domain. These measures reduce the risk of spoofing and strengthen your reputation with email providers

The three key authentication protocols that must be set up are: 

• Sender Policy Framework (SPF)
• DomainKeys Identified Mail (DKIM)
• Domain-based Message Authentication, Reporting & Conformance (DMARC). 

2. Validate Emails and Maintain Healthy Lists

A healthy email list is essential for strong deliverability and engagement in outbound email. Sourcing your data from reputable providers is a key first step—ensure the contacts are valid and within your target audience, and remove all users from your lists with invalid emails, and those who are frequent spam reporters, or those who have low engagement scores.

If you notice low deliverability, your contact lists are an excellent place to start. There may be harmful emails that need to be removed or emails that were previously safe to target but no longer are–after all, 30% of subscribers will change their email addresses annually. 

List hygiene has now evolved into a regular risk analysis of email lists, so clean up your lists regularly–we recommend you do this at least once a month. 

3. Make It Easy to Unsubscribe

One of the best ways to avoid winding up in the Spam folder is to ensure you have an easy way of allowing users to unsubscribe or opt out from your emails. This allows contacts who no longer want to receive your emails to quickly stop receiving them. Making it difficult for users to unsubscribe can lead to frustration for the users and will increase the chances that they report you as spam—hindering your email deliverability rates in the long run. One-click unsubscribe is now a mandatory requirement for companies who are sending certain numbers of emails a day, according to Google Sender Guidelines released in 2024. 

By only sending emails to those who wish to engage, you are increasing the chances of your emails being positively engaged with.

If you are sending emails like product newsletters, or marketing automation to a list of subscribers, there are a couple of ways to ensure you only send emails out to engaged users:

1. Double-opt in: Send out periodic emails throughout the year asking your subscribers if they’re still interested. Doing this will help ensure you maintain a list of interested subscribers who are more likely to engage with your emails as they are sent out actively.
2. Sunsetting policy: If you are looking to reengage users or weed out those who could harm your engagement metrics, you could offer a ‘final notice’ style email, asking users to open the email if they wish to keep receiving them from you.

Source: Allegrow email received from Slidebean 

4. Carry Out Contact Risk Analysis

While it’s important to verify email addresses, it's equally important to evaluate the risks associated with your contacts. Even if you’re gathering verified email addresses from legitimate third parties, your deliverability rate can be harmed if the users are prone to marking emails as spam, frequently bouncing, or showing no interest in engaging with your content.

Equally, Inbound contacts can carry risks too. Whether your contacts come from form fills, event registrations, or cold email lists, it’s crucial you treat all contacts with the same level of scrutiny. 

Conducting a regular and robust risk analysis of your lists helps you identify and remove these problematic contacts before you send out your campaigns and cadences. Tools like Safety Net Everywhere make this process easy.

5. Use a Subdomain(s)

Using a subdomain for email outreach offers greater control over sender reputation and reduces risks to your core domain. Subdomains maintain separate sender reputation scores, ensuring that outbound emails, transactional messages, or any email marketing activity won't negatively impact critical communications, like sending proposals and contracts to new clients. This separation safeguards your overall deliverability and mitigates the risks of outbound activities.

Subdomains also provide a slight ‘cushion’ in the case that something goes wrong. It’s easier to isolate and resolve the issue without disrupting your main domain. Additionally, using subdomains improves analytics by allowing businesses to track and compare the performance of different campaigns and departments. This makes it easier to identify and address any deliverability issues, supporting sustainable long-term, scaleable email strategies.

6. Monitor domain reputation

Email providers now rely more heavily on domain reputation, over IP reputation, as a dependable metric to evaluate a sender's engagement and history. Email domain reputation is determined by how recipients interact with your emails, rather than your domain’s performance in search engines. Domains that consistently achieve high levels of engagement will build a strong domain reputation, while those with low engagement will see their reputation decline, which will ultimately impact deliverability.

7. Keep Sequences Short 

It may seem counterintuitive, but less can often be more—particularly with email outreach. Sending messages to recipients who are unlikely to engage, especially on a large scale, can cause more harm than benefit.

For Outbound, sending shorter email sequences allows teams to test content and see if there is a good fit (or not) quickly. This way, the email messages can be revised, or reps can quickly move on to targeting contacts who will be a better fit.

From a marketing perspective, the same principles can be applied by making follow-ups and automation very specific to the action or conversion completed by a user segment. If the subscribers engage in a short campaign, they might be marketing-qualified and ready to be shared with the Sales team. If there is no engagement, the email campaigns or the ebook should be revised for content intent.

8. Write ‘Boring’ Subject Lines

Subject lines play a vital role in determining whether your emails get placed in the user’s primary inbox in two ways:

1. Spam Triggers: Subject lines containing specific keywords or spammy phrases can get flagged, causing emails to land in spam or be blocked entirely.
2. Engagement Impact: Unoptimized subject lines are less likely to be opened, leading to lower engagement rates. Over time, consistently poor engagement increases the chances of your emails being routed to the spam folder.

While it might seem tempting to use flashy, salesy, or overly emotive subject lines to boost open rates, a straightforward approach is often more effective. Clear, simple subject lines that accurately reflect the email’s content perform better and avoid triggering spam filters.

At Allegrow, we’ve tested countless subject lines and found that shorter ones perform best—3 to 5 words tend to drive higher engagement, with more ‘boring’ subject lines outperforming those that try too hard to engage recipients.

E.g. Instead of ‘"Trouble qualifying candidates, (Name)?", try opting for something like "(Company) Job Spec".

9. Provide a Notifications Preference Center

After your recipients opt-in to receive your emails, offer them a preference center where they can choose how often they want to hear from your brand. This approach gives them control, leading to greater satisfaction. Happy recipients are more likely to engage with your emails—a factor that ESPs pay close attention to.

10. Set Up Custom Tracking

Custom tracking domains allow you to send links and images (if included) through your own domain rather than a shared one, helping maintain strong deliverability. 

This is also important as we see ESPs like Gmail start to highlight images and tracking pixels as potential spam. 

To set this up, you need to add a CNAME record to your DNS settings using the values provided by your email host.

11. Warm Up Your Domains

Before sending a high volume of emails, it’s important to warm up your domain. Start by sending small amounts to segmented portions of your list, gradually increasing the volume over several weeks.

This approach helps you build and maintain a positive reputation with ESPs. While manual warm-up can be time-consuming, automated tools can simplify the process by mimicking human-like interactions with your inbox.

12. Clean & Segment Your Email List

Maintaining a clean list is essential, as it directly impacts the likelihood of your emails reaching your prospects’ inboxes. We recommend cleaning your list at least every 30 days. The more effectively you segment your prospects, the better you can target and engage them. Segmentation also allows for deeper content personalization and helps schedule emails to align with different time zones and countries.

Source: Allegrow Safety Net risk analysis for US segment

13. Personalize & Optimize Your Email Content

Content reputation plays a key role in how spam filters assess your domain’s reputation. By following email deliverability best practices, you can craft messages that are more likely to be positively received by ESPs, improving deliverability.

We’re also noticing a rise in senders conducting proactive Content A/B risk analysis—sending test emails to servers before reaching real users. This helps identify which content is less likely to trigger spam filters, reducing the risk of damaging deliverability.

Sending personalized, relevant emails can boost your deliverability, increase engagement, and build trust with your subscribers.

Avoid generic content—no one appreciates it, and in cold emailing, no one will bother reading it. Your goal should be to show recipients that you understand their problems and are the ones who can solve them. This connection is why personalizing your cold emails is crucial. You can enhance personalization with tools like:

• Merge tags
• Spintax
• Breaking preview text patterns - try changing the order of personalization tags and using negative phrases to catch the attention of users

14. Limit Use of Links & Attachments

It's best to avoid overloading your emails with links, especially when you're unfamiliar to the recipient. Including too many links, images, or videos can increase the email size and negatively affect deliverability.

If you need to send files or documents, it's better to host them on a CMS (Content Management System) and share a link instead of attaching the files. However, remember to follow link-sharing best practices—avoid including links in your initial emails.

15. Use No-Reply Emails with Caution

In addition to causing user frustration due to the inability to connect, no-reply emails can also further harm your reputation. ESPs may interpret lack of responses or engagement with these emails, as an indicator that these emails are spam. 

If you are going to use ‘no-reply’ emails for specific user transactions, consider warming up and using a separate subdomain for the no-reply use case. 

E.g. For all account setup and password-related no replies, you could use exclusively, no-reply@accounts.domain.com.

See more guidance on using subdomains here.

16. Monitor Your Email Metrics

Tracking your email performance metrics is crucial for maintaining and improving deliverability.

Here’s why it’s important:

• Identify issues early: Regular monitoring helps you catch potential deliverability problems before they escalate.
• Track improvements: Analyzing metrics over time lets you see how your deliverability efforts are paying off.
• Optimize your strategy: Use data-driven insights to fine-tune your email marketing tactics.

Key email metrics to keep an eye on:

• Bounce rate: High bounce rates can negatively affect your sender reputation. Monitor both hard and soft bounces.
• Spam complaint rate: A rise in complaints signals that your content or sending practices may need to be adjusted.
• Response and click-through rates: While not direct deliverability indicators, these engagement metrics affect how ESPs view your emails.
• Inbox placement rate: This shows what percentage of your emails successfully land in the inbox.

What Affects Email Deliverability Rate?

Email Service Providers Are Key Players in Email Deliverability

When it comes to email deliverability, one of the biggest enemies you face is the Email Service Providers (ESPs). ESPs have various tools to keep spam from reaching the Inbox. Unfortunately, these tools can directly impact your email deliverability since the ESPs have many emails to manage. 

ESPs Set Sending Limits for All Senders

ESPs set a sending limit for all senders. For example, Gmail allows you to send 500 emails a day, whereas Outlook caps at 1,000. Your email will sustain a soft bounce when they believe you have reached this sending limit within a certain period. This number may be set daily or weekly, depending on your email frequency. 

Some providers, like Gmail, will significantly lower your daily limit if your emails are frequently reported as spam and continuously surpassing daily limits will put you at risk of account suspension.

ESPs May Block Your Emails

ESPs may block your emails. This usually results from recipients marking your mail as spam or having your email hard bounce repeatedly. 

Although your email may be reported as delivered, there is a chance this email is just landing in spam, which means that important emails to existing customers or leads you’ve previously engaged with over longer sales cycles could start to land in spam. 

The Google Sender Guidelines state that spam report rate should be under 0.3%, but this metric is quite hard to accurately track, however by looking at metrics like bounce rate, it can be assumed that if your bounce rate exceeds 2-3%, your emails are likely ending up in spam. 

If your emails are ending up in spam, you need to start from square one and work on correctly throttling and warming up your domain.

Engagement from Recipients Is Important

Engagement from your recipients is essential. If your recipient is receiving your emails but failing to open them, this alerts the ESP that you may need to follow positive sending tactics. This means your emails go to the Spam folder. This can have a direct negative impact on your sender’s reputation. In many cases, eliminating inactive contacts is better than waiting for them to come around. It is better to have a smaller list of active subscribers than a more extensive list, with the bulk inactive. 

Emails Landing in Spam 

Even though the "deliverability rate" from your email provider may not specifically highlight it, emails landing in spam could be the underlying cause of low engagement. If recipients aren’t seeing your messages because they’re flagged as spam, they can’t engage with them. This issue can arise due to a poor sender reputation, lack of domain warm-up, or overly promotional language. Regularly monitoring spam placement and adjusting your sending practices can ensure your messages reach the intended inbox.

Why Email Deliverability Matters In Email Outreach?

Good email deliverability is crucial to obtain maximum ROI on your outreach efforts are practical. You work hard to craft emails that will appeal to your audience, not to mention the hard work that goes into building an email list, so you want your emails to make it into inboxes where they will be seen and engaged with. Your emails must meet several requirements to pass the mailbox providers’ filters and achieve good deliverability. 

Many emails get lost in a spam folder because of a poorly optimized subject line or lack of user engagement. Improving your email deliverability can help you gauge the percentage of your audience you’re reaching and avoid spam placement issues. You can troubleshoot any deliverability problems to learn whether your email address validity, sender reputation, email content, or something else is the cause.

How Allegrow Enhances Email Deliverability for Sales and Marketing Teams

Facing challenges with ESPs impacting your email deliverability? Allegrow can help you navigate sending limits, avoid spam folder pitfalls, and boost recipient engagement, with tools that empower teams to mitigate risk in their email outreach and optimize deliverability to make the most out of email as a channel for revenue. 

Related Reading

• Top 10 Email Deliverability Tools