How to Improve Email Deliverability: 7 Tips for Inbox Placement

Improve Email Deliverability, You crafted the perfect email campaign – great content, a compelling offer – but it doesn’t matter if those emails don’t land in your recipients’ inboxes. Email deliverability (your ability to reach the inbox rather than spam or promotions) is the crucial foundation of email success. The good news? There are concrete steps you can take to improve it. Here are 7 essential tips to boost your deliverability and get your emails where they belong: the inbox!

Improve Email Deliverability

1. Authenticate Your Sending Domain

Think of email authentication as a passport for your emails – it proves to mailbox providers that you are who you say you are and not an imposter or spammer. The core protocols are SPF, DKIM, and DMARC:

SPF (Sender Policy Framework): This is a DNS record that lists which IPs/servers are allowed to send emails for your domain. It helps ISPs verify, “Was this email sent from an authorized server?” Set up an SPF record that includes all the services you use to send email (your ESP, your own mail server, etc.).
DKIM (DomainKeys Identified Mail): This adds a digital signature to your emails that receivers can validate against a public key in your DNS. In plain terms, it’s like sealing your email with a wax stamp that proves it hasn’t been tampered with and is legitimately from your domain. Enable DKIM signing in your email service – most provide a pair of DNS records to publish for the keys.
DMARC (Domain-based Message Authentication, Reporting & Conformance): This builds on SPF/DKIM. It’s a policy you publish telling ISPs how to handle emails that fail SPF/DKIM and provides you reports. A basic DMARC record (p=none) just asks for reports, while p=quarantine or reject tells ISPs to spam or reject mails that fail checks. For 2025, it’s recommended to move toward an enforced policy (quarantine/reject) once you’re sure authentication is set up well.

Why is this so important now? Inbox providers have made authentication pretty much mandatory for good deliverability. In fact, Google, Yahoo, and Microsoft have been rolling out stricter requirements – e.g., by early 2025 Google and Yahoo require valid SPF/DKIM for high-volume senders, and Microsoft announced that by May 2025 any domain sending >5,000 emails/day to Outlook/Hotmail must have proper SPF, DKIM, DMARC or risk junking. Essentially, if you’re not authenticated, your emails might be outright rejected or silently dropped. So this is step one for inbox placement.

Tip: After setting these up, use tools like Google’s CheckMX or MailTester to verify everything is correct. And consider implementing BIMI (Brand Indicators for Message Identification) once DMARC is at enforcement. BIMI shows your brand’s logo in some email clients, and though mostly a branding perk, it requires those authentication pieces to be in place, acting as a trust signal.

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2. Use a Reputable Sending Domain (and Warm It Up)

Not all domains are equal in the eyes of spam filters. Using a custom domain (your own) rather than a generic free domain (like @gmail.com) for bulk emails is highly recommended – it looks professional and you can build a reputation on it. Ensure the domain you use hasn’t been used for spam in the past. If you’re using a new domain or subdomain for cold outreach or newsletters, do a warm-up:

Start by sending low volumes (maybe a few dozen emails/day) and gradually increase over a few weeks. Sudden large sends from a new domain/IP are a red flag for spam filters.
During warm-up, focus on sending to your most engaged contacts (who will likely open and click), because positive engagement early on boosts your domain’s reputation.
There are automated warm-up services (e.g., Lemwarm, Warmbox) that can send simulated emails between mailboxes to “prime” your domain – these can help if you’re doing cold email sending, though they should be used carefully.

Also, consider using a separate subdomain for mass emailing if you do a lot of it, to protect your main domain’s reputation (e.g., newsletters from @news.yourdomain.com while your personal one-to-one emails use @yourdomain.com). Many companies do this to isolate risk.

Reputation monitoring: Keep an eye on your sender reputation. Google postmaster tools (for Gmail) and Microsoft SNDS can show you reputation and any issues. If you see a dip, it might be due to spam complaints or bounces – which brings us to our next tip.

3. Maintain Pristine Email List Hygiene

This one cannot be overstated: sending to bad or disinterested addresses will wreck your deliverability. ISPs now heavily factor engagement and list quality into filtering decisions. Here’s how to keep your list clean:

Verify emails before sending: Use an email verification tool (like Sendrella’s service or others) to remove invalid addresses, typos, and spam traps. Sending to a bunch of nonexistent addresses (hard bounces) is a surefire way to get on mailbox providers’ naughty lists. Microsoft’s guidelines explicitly urge senders to “remove invalid addresses regularly”. So do it!
Remove chronic non-engagers: If a segment of your list hasn’t opened or clicked an email in, say, 6-12 months, consider removing or at least sunsetting them. Low engagement rates among your recipients tell ISPs that your content might be unwanted. By focusing only on those who engage, you improve your sender reputation. (Some providers like Gmail track user-level engagement – if many recipients ignore/delete your mails, Gmail will start treating all your mail as less important).
Watch out for spam traps: These are addresses used by ISPs to catch senders with poor practices (e.g., an old unused address recycled as trap, or a fake address published online). You won’t know them by sight, but by verifying and removing unengaged contacts, you minimize the risk. If you suddenly see an increase in blocklists or weird bounce messages indicating spam trap, you may have one – at that point, a deeper list audit might be needed.
Don’t buy or rent lists: It might be tempting to quickly scale your reach, but purchased lists are typically full of garbage (invalids, traps, and people who never opted in). Using them is almost guaranteed to hurt deliverability and often violates anti-spam laws. Organic list growth and confirmed opt-ins are the way to go.

By keeping a squeaky clean list, you’re signaling to providers “I only send mail to people who want it.” The result? Higher inbox placement and fewer bounces/spam flags. It’s been shown that simply scrubbing out inactive or bad emails can significantly boost deliverability – one source notes a clean list can improve deliverability by up to 25%. So this is your low-hanging fruit.

(On Sendrella’s platform, we have an Email Bounce Checker and list cleaning tools to help with this – check the Features page.)

4. Send Relevant, Personalized Content (Avoid Spam Triggers)

Even if you do everything technical right, what’s inside your emails matters a lot. Spam filters (and recipients) judge your emails by content and relevance:

Avoid known spam trigger words/phrases, especially in the subject line. Words like “FREE!!!”, “Urgent”, “Act Now”, excessive use of $$$, and all-caps or too many exclamation marks can trip filters (particularly on older spam filter systems). Modern filters are more context-aware but it’s still wise not to sound like a 2005 Viagra spam email.
Personalize when possible: Emails that read like a personal one-to-one message tend to get better treatment. Use the recipient’s name, reference their behavior or preferences if appropriate. Also segment your list so you send targeted content that each group actually finds valuable. As one expert succinctly put it: “Don’t irritate people and spam filters. We want our prospects to like our emails.” Relevant, interesting content = higher engagement = better deliverability.
Proper text-to-image ratio: All-image emails or emails that are one giant image with little text are a no-no. Many filters flag those because spammers often hide text in images. Include a balanced amount of HTML text. Aim for at least 60% text vs 40% images (and make sure to have alt text for images).
Check your HTML code: Poorly coded HTML emails (like unclosed tags, or using lots of old-school <font> tags) can trigger spam filters. Use clean, modern email templates (most ESPs provide these).
Include a clear unsubscribe link (and make sure it’s working!). Nothing will generate spam complaints faster than not giving an easy opt-out. And, as of 2024/2025, providers like Gmail expect you to honor opt-outs fast – Gmail is even showing “unsubscribe suggestions” to users for senders with low engagement. Microsoft and Google are actually factoring in whether people use your unsubscribe link (or mark you spam) as signals. Having an unsubscribe that’s one-click and easy to find is actually a positive for deliverability – it’s better they unsubscribe than hit “Report Spam”.
Don’t be “too salesy” without value: If every email is a hard sell, people may ignore or spam-bin them. Mix in informational or helpful content. Also, misleading subject lines or clickbait that doesn’t match the email content will get you spam reports – and a few of those can tank you (remember, a recipient marking your mail as spam is a strong negative signal for that provider’s algorithm).

One more thing under content: be careful with links. Use a consistent domain for your links (if you use click tracking, consider a branded tracking domain). Too many different domains or particularly blacklisted domains in your email can trigger filters. And obviously, never link to known bad sites. Some spam filters like Barracuda will check the reputation of URLs in your email.

5. Warm Up and Monitor Your Sending IP (If applicable)

If you’re sending via your own IP (or a dedicated IP address provided by your ESP), you need to be mindful of its reputation. New IPs have no reputation, which means large volumes from them look suspicious until they build credibility. Here’s what to do:

Warm up the IP just like warming a domain – gradually increase sending over time, starting with your most engaged recipients. Spread out your sends (don’t do huge bursts at 4am – send at times recipients are likely to open).
Monitor IP reputation: Use services like SenderScore (Validity) to check your IP’s score. Also, check blacklists periodically (MXToolbox blacklist check can scan dozens of common blocklists). If you see a blacklist listing, investigate why and request delisting once the issue is fixed.
Maintain consistent volume and sending cadence: Big spikes can trigger throttling. ISPs like consistency. If you plan a send of 100k and normally you send 10k, consider ramping up over a few days.
Consider a dedicated IP if you send very high volume and need control – but only do this if you can keep volume consistent. For smaller senders, sharing IPs with others via a reputable ESP is usually fine (the ESP will manage the IP reputation). If you go dedicated, all the above warm-up and monitoring is on you.

If you’re using a popular ESP (Mailchimp, Sendgrid, etc.) on a shared IP pool and your volume is modest, you might not have much control over IP. In that case, focus on the other tips (domain, content, etc.). But still monitor: if their pool has issues, you might consider moving or getting a private IP.

6. Focus on Engagement Signals

As hinted in earlier tips, engagement is the new currency of deliverability. ISPs like Gmail use engagement-based filtering – meaning if users often delete your emails without reading, or never open them, Gmail will start placing those emails in Promotions or Spam. Conversely, if users consistently open, reply, click, move your emails to primary inbox, etc., your chances improve. Here’s how to boost engagement (beyond having great content):

Encourage replies: Especially for things like welcome emails or cold outreach, asking the recipient to reply (and even asking a question to prompt it) can help. User replies are a positive indicator to ISPs. For example, in cold B2B outreach, sometimes senders will intentionally ask a simple question to get a reply, which then makes future emails more likely to hit inbox.
Send at the right time: Use analytics or AI to determine when each contact is most likely to open email (many ESPs now offer send-time optimization). Sending when your audience is online and checking mail means more opens, which signals providers quickly that “hey, people like this email.”
Use double opt-in for sign-ups so that your list is super engaged from the start (those who bother to confirm are typically higher engagement).
Re-engage or remove dormant subscribers (covered in list hygiene, but reiterating). Before removing, you might try a re-engagement campaign: “We miss you – do you still want our emails?” Sometimes they just need a nudge. If they still don’t engage, it’s time to say goodbye. This helps your overall metrics as explained.
Avoid spam complaints at all costs: If you notice even a handful of complaints, take it seriously. Perhaps your unsubscribe link is hard to find? Or the content frequency is too high? Users hitting “Report Spam” is one of the worst blows to deliverability. Keep complaint rates well under 0.1% (1 in 1,000) – many ESPs might alert you if you exceed that. To minimize complaints: only email people who opted in, set expectations (tell them what you’ll send and how often up front), and make unsubscribing painless.

One tactic: Provide a email preferences center in your unsubscribe link. Some recipients don’t want to fully unsubscribe but maybe want less frequent emails. Giving them that option might save some relationships and reduce spam reports.

Remember, engagement is not just a result of good deliverability, it’s now a cause of it. It’s a feedback loop: better placement -> more engagement -> even better placement. We want to get into that positive spiral.

7. Monitor Your Deliverability and Adapt

Finally, treat deliverability management as an ongoing process:

Use analytics and tools: Monitor open rates by domain (are your Gmail open rates tanking but Yahoo is fine? That indicates an issue specific to Gmail deliverability). Use seed testing tools like MailTester or GlockApps to see if test emails land in spam across various providers. Services like MailGenius or Warmy provide insights on spam triggers. Litmus or Email on Acid can show you if you’re in Gmail’s Promotions tab vs Primary for their seed accounts.
Check feedback loop data: For ESPs that provide feedback loop reports (mostly for spam complaints on certain ISPs like Yahoo, AOL), review those. For example, if you use Amazon SES or another, you can get alerts when someone marks you spam (on ISPs that support it). Immediately remove those folks – you don’t want to keep emailing someone who hit spam on you.
Stay updated on ISP guidelines: ISPs occasionally update their best practice guidelines (e.g., Gmail’s Bulk Sender Guidelines, Microsoft’s sender best practices). For instance, Microsoft’s 2025 updates we noted about authentication and list hygiene. Keep an eye on those changes (following blogs like ours – Sendrella – or deliverability experts on LinkedIn can help you stay informed).
Test and iterate: If you make a change (say, new subject line style, or switched sending IPs), watch your metrics. Did deliverability drop or improve? Sometimes small tweaks can have effects. For example, simply moving from an image-heavy template to a more text-based personal-looking email can improve Gmail inboxing dramatically (woodpecker.co). Always be willing to adapt your design or strategy based on these observations.
Consider using a dedicated deliverability tool or service: If email is mission-critical and you have thousands on your list, investing in something like Validity’s Everest or InboxAlly or hiring a deliverability consultant might be worth it. They can provide deep insights (like seed list inbox placement rates, blocklist monitoring, etc.). But for many, that might be overkill – still, know that these resources exist if needed.

In summary, improving deliverability is about building trust – with both the mail providers’ algorithms and your recipients. Authenticate your emails, send to people who want them, provide valuable content at a reasonable frequency, and promptly address any issues that arise. By following the seven tips above, you’ll greatly increase the chances that your carefully crafted emails actually reach your audience’s eyes.

Deliverability can feel technical, but it boils down to respect and quality. Respect the inbox (permission and privacy), and maintain quality in your sending practices. Do that, and you’ll find your emails landing in the inbox more often – meaning all your other email efforts can pay off.

Need help with deliverability? Sendrella isn’t just about verification – our platform offers tools and guides for maintaining sender reputation (see our Blog posts on bounce management and content tips). And if you’re unsure about your current status, you can use Sendrella’s free tools or reach out to our support for pointers – we’re happy to help you get more emails delivered!