How to Improve Email Deliverability to Gmail and Outlook

TL;DR: To improve email deliverability to Gmail and Outlook, authenticate your domain with SPF, DKIM, and DMARC, clean your list regularly, keep spam complaint rates below 0.1%, warm up new IPs gradually, and monitor sender reputation using Google Postmaster Tools and Microsoft SNDS. These steps ensure more emails reach the inbox instead of spam folders.

Email deliverability is a performance metric that measures whether your sent emails successfully reach recipients’ inboxes rather than being filtered into spam folders or blocked entirely. Nearly 1 in 5 legitimate marketing emails never reach the inbox, according to Validity’s 2023 Email Deliverability Benchmark Report, roughly 20% of permission-based emails get lost in spam folders or blocked entirely. If you’ve ever wondered why your beautifully crafted campaigns are getting crickets instead of clicks, deliverability might be the silent killer lurking behind the scenes.

Gmail and Microsoft Outlook (including Outlook.com, Hotmail, and Microsoft 365) collectively dominate the email client market, accounting for over 60% of global email opens. So if your emails aren’t landing in their inboxes, you’ve got a serious problem. But don’t panic, this blog is your roadmap to inbox glory. Let’s break down exactly what you can do to make Gmail and Outlook love your emails as much as your subscribers should.

Why does email deliverability matter for marketing ROI?

Email deliverability matters because it directly determines how much revenue your email campagins generate, email marketing produces an average return of $36 for every $1 spent (Litmus, 2023), but that figure only holds when messages actually reach the inbox, making deliverability the foundation of every dollar earned through email campaigns.

• Revenue impact: If 20% of your emails miss the inbox, you’re potentially losing 20% of your email-driven revenue. For a business generating $100K/month from email, that’s $20,000 vanishing into the digital void.
• Sender reputation damage: Poor deliverability creates a vicious cycle. Low engagement signals to Gmail and Outlook that your emails aren’t wanted, which further tanks your placement.
• Wasted resources: You’re paying for every email you send, the copywriting, the design, the platform costs. Spam folder placement means you’re literally paying to be ignored.

Bottom line? Deliverability isn’t a “nice to have.” It’s the difference between an email program that prints money and one that burns it.

How do Gmail and Outlook filter incoming emails?

Gmail and Outlook use sophisticated and largely proprietary algorithms to decide whether your email deserves inbox placement, the spam folder, or the dreaded “Promotions” tab, they evaluate sender authentication, user engagement signals, complaint rates, and content quality, and understanding these factors is the first step toward consistently landing in the inbox.

Gmail’s filtering priorities

Gmail places heavy emphasis on user engagement. It tracks whether recipients open your emails, click links, reply, move you out of spam, or, the worst signal, mark you as spam. Google’s 2024 sender requirements also mandate proper authentication (SPF, DKIM, DMARC) for anyone sending more than 5,000 emails per day to Gmail accounts.

Outlook’s filtering priorities

Microsoft’s SmartScreen filter and their broader anti-spam infrastructure lean heavily on sender reputation, complaint rates, and spam trap hits. Outlook also uses its own Sender Reputation Data (SRD) program, where real users vote on whether your emails are spam. Think of it as Yelp reviews for your sending behaviour. For more details, see Microsoft’s Postmaster tools and guidelines.

What are the 10 steps to improve email deliverability?

The following ten actionable steps cover authentication, list hygiene, reputation management, and content optimisation, together they form a comprehensive framework that addresses every major factor Gmail and Outlook evaluate when deciding whether to deliver your emails to the inbox or divert them to spam.

1. Authenticate your emails like your reputation depends on it (because it does)

Email authentication is non-negotiable. Set up these three protocols, all of which are defined in standards published by the Internet Engineering Task Force (IETF):

• SPF (Sender Policy Framework): SPF is a DNS-based protocol that specifies which IP addresses are authorised to send email on behalf of your domain.
• DKIM (DomainKeys Identified Mail): Adds a digital signature to your emails, proving they haven’t been tampered with in transit.
• DMARC (Domain-based Message Authentication, Reporting & Conformance): Tells Gmail and Outlook what to do when emails fail SPF or DKIM checks. Start with a monitoring policy (p=none) and work toward p=reject.

As of February 2024, Google requires all bulk senders to have SPF, DKIM, and DMARC properly configured. Microsoft has announced similar requirements taking effect in 2025. The NIST Special Publication on Trustworthy Email also recommends implementing all three protocols as a baseline security practice. If you haven’t set these up yet, stop reading and do it now. Seriously. We’ll wait.

2. Clean your email list ruthlessly

A dirty list is a deliverability death sentence. Email lists naturally decay at a rate of about 22.5% per year (HubSpot). People change jobs, abandon email addresses, and forget they ever signed up for your newsletter.

Here’s what to do:

• Remove hard bounces immediately after every send. (TouchBasePro manages this for you)
• Suppress subscribers who haven’t engaged in 90–120 days (or run a re-engagement campaign first).
• Use an email verification service to identify invalid addresses, spam traps, and role-based emails before they damage your reputation.
• Never, ever buy email lists. Just don’t. It’s the email marketing equivalent of setting your house on fire to stay warm.

3. Warm up new sending domains and IPs

If you’re sending from a new domain or a dedicated IP address, you need to warm it up gradually. Think of it like building credit, you can’t walk into a bank with no history and ask for a million-rand loan.

Start by sending small volumes (50–200 emails per day) to your most engaged subscribers, the ones who always open and click. Gradually increase volume over 4–6 weeks. This builds positive sender reputation signals with Gmail and Outlook from day one.

4. Keep your spam complaint rate below 0.1%

Google explicitly states that senders should maintain a spam complaint rate below 0.10% and should never exceed 0.30%. Microsoft has similar thresholds. Even a small spike in complaints can tank your reputation for weeks.

To keep complaints low:

• Make your unsubscribe link visible and easy to use (one-click unsubscribe is now required by Google).
• Set clear expectations during signup about what subscribers will receive and how often.
• Segment your audience so you’re sending relevant content, not blasting everyone with everything.

5. Segment and personalise like a pro

Segmented email campaigns drive 30% more opens and 50% more click-throughs than unsegmented ones (Mailchimp). And higher engagement = better deliverability. It’s a beautiful positive feedback loop.

Segment by purchase history, engagement level, signup source, geographic location, or any data points meaningful to your business. Personalisation goes beyond “Hi [First_Name]”, tailor content, offers, and send times to individual subscriber behaviour.

6. Optimise your sending frequency and timing

Sending too frequently overwhelms subscribers and increases unsubscribes and complaints. Sending too rarely makes people forget who you are (which also increases complaints). Find the sweet spot by testing different frequencies and monitoring engagement metrics closely.

Pro tip: Let subscribers choose their preferred frequency during signup or through a preference centre. Giving people control dramatically reduces complaints.

7. Write subject lines that don’t scream “SPAM”

Avoid these spam-trigger patterns:

• ALL CAPS SUBJECT LINES (you’re not a monster).
• Excessive exclamation marks!!!!!!
• Misleading “Re:” or “Fwd:” prefixes.
• Overuse of words like “free,” “guaranteed,” “act now,” or “limited time” (a few are fine, stuffing them is not).

Instead, write subject lines that are clear, relevant, and genuinely interesting. A/B test regularly to learn what resonates with your audience.

8. Maintain a healthy text-to-image ratio

Emails that are 100% images with no text are a red flag for spam filters. Aim for a 60/40 text-to-image ratio. Always include alt text on images, and make sure your message is readable even if images don’t load (Outlook blocks images by default for many users).

9. Monitor your sender reputation continuously

A sender reputation is a score that mailbox providers assign to your sending domain and IP address based on your historical email behaviour. You can’t fix what you can’t see. Use these free tools to keep tabs on your reputation:

• Google Postmaster Tools: Essential for monitoring your domain and IP reputation with Gmail, spam complaint rates, and authentication status.
• Microsoft SNDS (Smart Network Data Services): Provides data on your sending reputation, complaint rates, and spam trap hits within the Microsoft ecosystem.
• MXToolbox: Check if your IP or domain is on any major blacklists.

Set up a regular cadence, weekly at minimum, to review these dashboards and catch issues before they snowball.

10. Implement a sunset policy for inactive subscribers

A sunset policy is a systematic process that removes or suppresses subscribers who have stopped engaging with your emails over a defined period. This one hurts, but it’s necessary. Subscribers who haven’t opened or clicked an email in 6–12 months are dragging down your engagement metrics and, by extension, your deliverability.

Run a re-engagement campaign first (a “We miss you!” email or a special offer). If they still don’t respond after 2–3 attempts, move them to a suppression list. Your list will be smaller, but your results will be dramatically better. Quality over quantity, always.

Is Gmail’s promotions tab actually bad for deliverability?

Gmail’s Promotions tab is not the enemy many marketers assume it to be, in fact, 68% of Gmail users check their Promotions tab regularly, and emails there often have higher purchase intent because users are actively browsing deals and content, which means landing in Promotions is vastly better than landing in spam.

The real enemy is the spam folder. Focus your energy on staying out of spam, and don’t lose sleep over the Promotions tab.

How should you build a deliverability action plan?

Building a deliverability action plan requires prioritising authentication and list hygiene first, then layering on ongoing reputation monitoring and content optimisation, start with the quick technical wins this week, expand to list management this month, and commit to continuous improvement as a permanent practice for sustainable inbox placement.

1. This week: Verify your SPF, DKIM, and DMARC records are properly configured.
2. This month: Clean your list, remove inactive subscribers, and set up Google Postmaster Tools and Microsoft SNDS.
3. Ongoing: Segment your audience, personalise your content, monitor your reputation dashboards, and test relentlessly.

Email deliverability is the invisible engine that powers every successful email marketing program. When you improve email deliverability, every campaign you send will work harder, reach further, and convert better. Ignore it, and you’re essentially shouting into the void, expensively.

Ready to improve email marketing? At TouchBasePro, we help marketers send smarter, land in more inboxes, and drive real results from every campaign. Get in touch with our team to learn how we can help you improve email deliverability and maximise your marketing ROI.