Do’s and Don’ts of Email Deliverability

Email marketers spend countless hours perfecting their designs, polishing subject lines, and crafting campaigns that feel personal and relevant. Yet none of that effort matters if the message never reaches the inbox. Deliverability has quietly become the deciding factor between a successful email campaign and one that struggles to get noticed. With mailbox providers using more advanced filtering systems and engagement signals than ever before, ensuring your emails land where they should is now a core part of email marketing, not an afterthought.

Deliverability may seem technical, but at its heart, it's about trust. When mailbox providers trust your domain, your list quality, and your sending patterns, your campaigns perform better. In this guide, we break down the do’s and don'ts of email deliverability, helping you understand what strengthens inbox placement and what silently weakens it.

What Is Email Deliverability?

Email deliverability is the ability of your emails to successfully reach your subscribers' inboxes, not just get "delivered" somewhere, but arrive where they will be seen. Landing in the inbox depends on several factors: your sending domain, your email list quality, your content, your authentication setup, and how mailbox providers like Google, Yahoo, Outlook, and Apple Mail evaluate your sender reputation. If you want better engagement and higher revenue from your campaigns, understanding and improving deliverability is essential. Now, let's check the do’s and don'ts of the email landscape.

Don'ts

1. Don't Purchase Email Lists

Buying email lists is the worst idea in 2025. Mailbox providers now use real-time AI-driven algorithms that immediately detect suspicious patterns linked to purchased lists. These lists often contain invalid emails, spam traps, role-based emails, and unengaged users who never opted in.

High bounce rates and spam complaints from these lists can instantly damage your sender reputation. Once your domain reputation suffers, recovery can take weeks or even months.

Let's take an example: a SaaS company bought a "targeted B2B list" of 30,000 contacts. Their first campaign had a 35% bounce rate, several users marked the email as spam, and their domain was throttled for days. Their transactional emails started going to spam as well, hurting real customers, not just their marketing campaigns.

Growing your list organically is the best method. Focus on signup forms, gated content, loyalty programs, or product onboarding flows. A smaller, engaged list is always more profitable than a large, unresponsive one.

2. Don't Send From A Free Domain

Using a free domain for your business, like Gmail.com or Yahoo.com, immediately signals to mailbox providers that your email may not be legitimate. Spammers commonly abuse these domains because they are easy to register and lack authentication capabilities. In 2025, DMARC enforcement policies from Google and Yahoo will make it even more restrictive. Email marketing platforms now reject campaigns from free domains altogether.

Investing in a custom domain for your business is essential. Not only does it make your brand look more professional, but it also allows you to set up authentication (SPF, DKIM, DMARC) that improves your trustworthiness with mailbox providers.

3. Don't Ignore High Bounce Rates

Many marketers still overlook bounce rates, assuming they are a regular part of email marketing. But consistent hard bounces, caused by invalid or undeliverable emails, are among the strongest negative signals you can send to mailbox providers. Ignoring bounce rates will harm your sender reputation faster than almost anything else.

If your bounce rate regularly exceeds 2%, it indicates something is wrong. You may be emailing outdated contacts, using a poorly maintained CRM, or missing regular list verification cycles. A healthy email program actively monitors and removes risky addresses before sending.

4. Don't Send Without Segmentation

Blasting your entire list with the same message is outdated and dangerous. Engagement-based filtering is now one of the most significant factors in inbox placement. If a large percentage of your list consistently ignores your emails, providers assume your content is irrelevant and may push future campaigns toward spam or promotions.

Poor segmentation causes:

• Lower open rates
• High unsubscribe rates
• Poor click-through rates
• Engagement decays over time

Instead of treating your audience as one large group, segment based on behavior, purchase history, frequency of interaction, or interests. Relevance is now a key requirement, not a bonus.

5. Don't Send Too Frequently Or Too Infrequently

Email frequency affects deliverability more than most marketers realize. Sending too many campaigns in a short period can lead to fatigue, complaints, and unsubscribes. Sending too few campaigns can cool engagement and prompt mailbox providers to downgrade your domain due to inactivity.

For example, sending 10 emails in 3 days after months of silence triggers red flags. Establishing a consistent, predictable cadence helps maintain steady engagement rates, which mailbox providers use to assess your sender reputation.

6. Don't Ignore Authentication Requirements

Authentication is mandatory in 2025. Unauthenticated email is treated as "unverified," and many inboxes now automatically block it. Without proper authentication, your campaigns may be flagged or rejected entirely. Not following authentication best practices is no longer a mistake; it's a deliverability failure.

7. Don't Continue Sending To Inactive Subscribers

It can be tempting to keep emailing your entire list for "reach," but sending to inactive users drains your engagement rates. If someone has not opened or clicked your emails in six months or more, mailbox providers assume your emails are irrelevant to that user. Continuous sending to inactive audiences increases the chances of spam filtering.

Instead, identify inactivity early and use re-engagement workflows to remove cold subscribers. This protects your reputation and improves your overall engagement.

Do's

1. Clean Your Lists Regularly

This principle remains just as critical today. Verifying your email lists with a trusted email verification solution like Emailable helps eliminate undeliverable, invalid, and risky email addresses before they damage your reputation. Regular verification also enables you to maintain a clean list over time, especially if your audience grows quickly or you collect emails from multiple channels.

A good practice is to verify your lists:

• Before major campaigns
• After importing old contacts
• Every 30–60 days for active senders

Clean lists make your campaigns healthier and safer, reducing bounce rates and improving inbox placement.

2. Maintain Strong Sender Reputation

Sender reputation is your domain's credit score in the eyes of mailbox providers. It is affected by your bounce rate, spam complaints, sending frequency, authentication setup, and engagement metrics. Maintaining a strong sender reputation is the foundation of good deliverability.

Mailbox providers track:

• How many users open your emails
• How many users delete without reading
• How many mark your emails as spam
• How many emails bounce
• How many times has your domain attempted risky sending patterns

If these signals are negative, providers may limit your visibility. If they're positive, your inbox placement strengthens over time.

3. Authenticate Your Domain Properly

Authentication is the backbone of deliverability. Setting up SPF, DKIM, and DMARC ensures mailbox providers can verify that you are the legitimate sender of the emails using your domain. Authentication directly translates to trust, and trust directly translates to deliverability.

4. Maintain Consistent Sending Patterns

Irregular sending behavior, such as sudden spikes or long gaps, makes it harder for mailbox providers to assess your trustworthiness. Maintaining a steady cadence stabilizes your engagement rates and builds a positive reputation. Consistency helps mailbox providers predict how many emails you typically send, to whom, and how recipients respond.

5. Craft Content That Signals Trust And Relevance

While deliverability is often about technical setup, content quality still matters. Emails with misleading subject lines, excessive capitalization, hidden text, broken links, or deceptive promotions are more likely to be filtered into spam.

Good content improves deliverability:

• Clear subject lines
• Personalized messaging
• Authentic sender names
• Clean HTML code
• Relevant offers

Mailbox providers track user reactions to your content. Good reactions strengthen your reputation over time.

6. Use Engagement To Your Advantage

Engagement-based filtering means mailbox providers favor emails that people actively interact with. Sending to your most engaged subscribers first, tailoring messages to behavior, and encouraging replies all help build strong signals.

Positive signals include:

• Opens
• Clicks
• Replies
• Moving emails to folders
• Marking emails as important

These signals help inbox algorithms push your emails to the primary inbox rather than promotions or spam.

7. Build Sunset Policies for Inactive Users

A sunset policy automatically removes subscribers who haven't interacted with your emails for a specified period. This preserves your engagement metrics and protects your reputation.

For example, you might sunset users after:

• 90 days of inactivity for newsletters
• 180 days for e-commerce audiences
• 12 months for long-lifecycle products

Removing inactive users keeps your email list healthy and engagement strong.

Conclusion

Creativity, strategy, and automation make email marketing exciting, but none of these benefits matter if your emails fail to reach your audience. Deliverability remains the invisible backbone of every successful campaign. When you combine technical authentication, list hygiene, thoughtful segmentation, consistent sending patterns, and a strong sender reputation, your email campaigns become significantly more powerful.

Email deliverability in 2025 is not just about avoiding mistakes; it's about building an ecosystem of trust with mailbox providers. Following the do's and don'ts above will help you consistently land in the inbox, improve your engagement rates, and strengthen your brand's long-term reputation.