Getting to the inbox is harder than it used to be. Inbox providers, Google, Microsoft, Yahoo, Apple, have tightened their filtering over the past few years, and the rules are now explicit enough that violating them means your mail goes to spam, or gets blocked entirely. This is not about clever copywriting. It is about infrastructure, list quality, and reputation signals that providers measure automatically.
Here are eight things that actually move the needle.
Quick answer: The fastest path to better deliverability is (1) authenticate with SPF, DKIM, and DMARC, (2) warm new domains gradually, (3) scrub bounced addresses, (4) use double opt-in, (5) clean up your copy and image ratio, (6) keep volume consistent, (7) make unsubscribing easy, and (8) monitor your sender reputation regularly with free tools like Google Postmaster Tools.
1. Authenticate with SPF, DKIM, and DMARC
SPF, DKIM, and DMARC are DNS-level records that prove you are the legitimate sender of an email, and missing any one of them gives inbox providers a reason to route your mail to spam.
SPF (Sender Policy Framework) is a DNS TXT record that lists the mail servers authorized to send on behalf of your domain. DKIM (DomainKeys Identified Mail) attaches a cryptographic signature to every message so the receiving server can confirm it was not altered in transit. DMARC (Domain-based Message Authentication, Reporting, and Conformance) tells providers what to do when a message fails SPF or DKIM, quarantine it, reject it, or deliver it, and sends you reports when failures happen.
All three work together. SPF and DKIM without DMARC means you have no policy enforced. DMARC without a passing SPF or DKIM alignment means DMARC fails anyway. Google's bulk sender requirements, published in 2024, mandate that senders above certain volume thresholds have all three configured correctly to reach Gmail inboxes. You can verify your current setup with Google's Email Sender Guidelines and the MX Toolbox suite.
Takeaway: Check your DNS records today. SPF, DKIM, and DMARC all need to pass before anything else on this list matters.
2. Warm Up New Domains and IPs Gradually
A brand-new sending domain has no reputation history, so you need to start with a small volume, a few dozen messages per day, and increase slowly over four to eight weeks before sending at full scale.
Inbox providers assign reputation scores to sending domains and dedicated IPs. A domain with zero history that suddenly sends 50,000 emails looks, to a spam filter, indistinguishable from a newly registered phishing domain. The fix is a warm-up schedule: start with small batches to your most engaged subscribers, people who open consistently, and double volume every few days as positive signals (opens, clicks, no complaints) accumulate.
If you are using a shared IP pool through a platform like Mailchimp, Klaviyo, or HubSpot, those platforms manage IP reputation on your behalf, but domain reputation is still yours to build. For dedicated IPs, common for high-volume senders above roughly 100,000 emails per month, the warm-up responsibility falls entirely on you.
Four to eight weeks is the realistic timeline. Rushing it to meet a campaign deadline is one of the most common reasons a new sending domain ends up on a blocklist in its first month.
Takeaway: Map out a warm-up schedule before you send a single campaign from a new domain. Start with your most engaged segment, not your full list.
3. Scrub Invalid and Bounced Addresses
Hard bounces above 2 percent are a threshold at which mailbox providers begin penalizing sender reputation, which is why regular list scrubbing is a deliverability requirement, not optional hygiene.
Email bounces come in two types. Soft bounces are temporary failures: a full inbox, a server timeout, a temporary block. Hard bounces are permanent: the address does not exist, the domain is gone, or the mailbox has been deactivated. Sending to hard-bounce addresses repeatedly tells providers your list is poorly maintained, and a high bounce rate is one of the faster ways to get your domain flagged.
Most email platforms will automatically suppress hard bounces after the first occurrence, but that is reactive. A proactive approach adds an email validation step before addresses even enter your list. Tools like ZeroBounce, NeverBounce, and Kickbox check addresses against known invalid patterns, spam traps, and disposable-email domains before you send.
If you are re-engaging a list that has not been emailed in six or more months, validate it before the campaign. Addresses that were valid a year ago may not be valid today, and spam-trap networks deliberately recycle abandoned addresses to catch senders with poor hygiene.
Takeaway: Run your list through a validation tool before any large send to a segment you have not emailed recently, not just after you see a bounce spike.
4. Use Double Opt-In to Protect List Quality
Double opt-in filters out typos, disposable addresses, and spam traps before they reach your list and damage your sender reputation.
Single opt-in adds a subscriber the moment they submit a form. Double opt-in sends a confirmation email first and only adds the subscriber when they click the link inside it. The result is a list composed entirely of people who confirmed a working email address and took a deliberate action to join.
The tradeoff is real: double opt-in reduces list growth rate because some people never confirm. But the addresses that do confirm are more likely to be real, more likely to engage, and far less likely to mark your mail as spam. For deliverability purposes, a smaller list with higher engagement is substantially more valuable than a larger list with lower engagement, because inbox providers weight engagement signals, especially Gmail, when deciding where to place your mail.
For B2B senders, double opt-in also creates a documented record that a subscriber requested your mail, which matters if a complaint is ever escalated.
Takeaway: Turn on double opt-in by default for any new list or lead magnet. The short-term dip in list size pays back in long-term inbox placement.
5. Avoid Spam-Trigger Words and Heavy Images
Spam filters score the content of your message, not just your authentication records. Subject lines and body copy loaded with words that pattern-match to promotional or deceptive email raise your spam score. So does a message that is 90 percent images with almost no text, which is a common technique used by spammers to hide their content from text-based filters.
You do not need to strip every promotional word from your copy. The goal is a reasonable balance: text-based copy that communicates your message clearly, images that support rather than replace the text, and a plain-text version of every email alongside the HTML version. Most major ESP (email service provider) platforms generate the plain-text version automatically, but verify yours is populated and readable, not blank.
A few practices worth building into your template QA process before sending:
- Preview the email in Gmail, Outlook, and Apple Mail, rendering differs.
- Check that your HTML-to-text ratio is not image-heavy.
- Avoid all-caps subject lines and excessive punctuation.
- Test with a tool like Mail-Tester or Litmus before campaigns go out to large segments.
Takeaway: Run every campaign through a pre-send content check. A deliverability problem that starts with a bad template affects every subscriber you have, not just one segment.
6. Keep a Consistent Sending Volume and Cadence
Inbox providers use behavioral patterns to distinguish legitimate senders from compromised accounts. A sender that mails weekly to a stable list looks predictable and trustworthy. A sender that disappears for two months and then blasts a 200,000-person list looks like a compromised account or a purchased list, both of which are spam patterns.
Consistency applies in both directions: do not go dark for long periods, and do not spike volume without a warm-up. If you have a legitimate reason to send a larger-than-usual campaign, a product launch, a seasonal push, ramp into it over a few sends rather than jumping directly to your maximum volume.
For senders who are growing their list quickly, this also means your sending volume should increase proportionally with list growth, not in sudden jumps. If your list doubles, do not immediately double the send volume in a single campaign.
Takeaway: Build a sending calendar and stick to it. Predictable patterns are a deliverability asset that builds over time.
7. Make Unsubscribing Easy to Reduce Complaints
Google and Yahoo require bulk senders to support one-click unsubscribe and to keep spam-complaint rates below 0.10 percent, per their 2024 sender requirements.
This is not a suggestion. Google's and Yahoo's 2024 bulk sender requirements explicitly mandate that senders above a certain volume threshold include a one-click unsubscribe mechanism using the List-Unsubscribe header, not just a link buried in the footer, but a machine-readable header that lets providers surface an unsubscribe option directly in the inbox UI. Most major ESPs add this header automatically, but confirm yours does.
The reason this matters for deliverability: when a subscriber cannot easily unsubscribe, they click "Report Spam" instead. Spam complaints are one of the heaviest negative signals inbox providers use to score your domain. Google Postmaster Tools, covered in item 8 below, shows your spam-complaint rate from Gmail's side. The threshold to stay well below is 0.10 percent, above that, inbox placement degrades. Above 0.30 percent, the consequences become severe.
A one-click unsubscribe also means the people who remain on your list actually want to be there, which improves your engagement metrics across the board.
Takeaway: Check that your ESP is sending the List-Unsubscribe header on every campaign and that the unsubscribe process requires no more than one click.
8. Monitor Sender Reputation and Engagement
Google Postmaster Tools is a free tool that shows your domain reputation, spam rate, and authentication pass rate directly from Gmail's perspective.
You cannot fix a deliverability problem you cannot see. Two free tools give you the clearest visibility into how the biggest providers are scoring your domain:
Google Postmaster Tools (postmaster.google.com) shows your domain reputation (High, Medium, Low, or Bad), your IP reputation, your spam rate as Gmail measures it, and your SPF/DKIM/DMARC authentication pass rates, all over time, so you can correlate reputation changes with specific campaigns. If your domain reputation drops from High to Medium after a particular send, that is your signal to investigate what changed.
Microsoft SNDS (Smart Network Data Services) at sendersupport.olc.protection.outlook.com provides similar data for Outlook and Hotmail delivery.
Beyond platform tools, watch your ESP's engagement data, open rates, click rates, and unsubscribe rates, segment by segment. Declining engagement in a segment is often a leading indicator of a reputation problem before it shows up in deliverability reports. Pull non-openers on a 90-day basis and either run a re-engagement campaign or suppress them before their inactivity drags down your overall metrics.
Takeaway: Set up Google Postmaster Tools today if you have not. It is free, takes 15 minutes to configure, and shows you exactly how Gmail is scoring your domain before problems escalate to a block.
Email deliverability is infrastructure. It is not a campaign tactic you run once, it is a system you build and maintain. Authentication, list hygiene, warming, content quality, volume consistency, unsubscribe mechanics, and reputation monitoring all work together. A gap in any one of them can offset progress in the rest.
If your tracking and marketing automation infrastructure needs an audit, not just email, but the full pipeline from click to conversion, the team at RGDM builds and monitors those systems. Book a strategy call and we will start with what is actually broken.
More in RGDM Insights.
Frequently Asked Questions
How do I improve email deliverability?
Start with the technical foundation: configure SPF, DKIM, and DMARC in your DNS, and verify all three pass using a tool like MX Toolbox. Then clean your list to remove hard bounces and invalid addresses, switch to double opt-in for new subscribers, and monitor your domain reputation with Google Postmaster Tools. Consistent sending cadence and easy unsubscribing keep your complaint rate low over time.
Why are my emails going to spam?
The most common causes are missing or misconfigured authentication records (SPF, DKIM, DMARC), a high spam-complaint rate from recipients clicking "Report Spam" instead of unsubscribing, a high bounce rate from invalid addresses on your list, or a sudden spike in sending volume that looks like atypical behavior to inbox providers. Google Postmaster Tools will show you your spam rate and domain reputation from Gmail's perspective, which is the fastest way to diagnose the issue.
What is a good deliverability rate?
Deliverability rate measures what percentage of your sent emails actually reach a recipient's mailbox (inbox or spam folder, as opposed to being rejected). Most practitioners aim for a deliverability rate above 95 percent, though the more actionable metric is inbox placement rate, the share that land in the inbox rather than the spam folder. Inbox placement is harder to measure without a tool like Litmus or Email on Acid, but your open rate trend is a useful proxy: a sudden drop in opens often indicates a shift in inbox placement.
How do I stop hitting the spam folder?
Check your authentication records first, a failing DMARC policy or a broken DKIM signature will suppress inbox placement immediately. Then look at your spam-complaint rate in Google Postmaster Tools; if it is above 0.10 percent, your unsubscribe flow needs to be easier and your list needs to be cleaned. If both are healthy, audit your content: image-heavy templates with minimal text, promotional subject-line patterns, and missing plain-text versions all raise spam-filter scores.
What is SPF, DKIM, or DMARC and do I need all three?
Yes, you need all three. SPF authorizes which servers can send mail for your domain. DKIM signs each message with a cryptographic key so receiving servers can verify it has not been altered. DMARC sets the policy for what happens when a message fails SPF or DKIM, and delivers reports back to you when failures occur. Google's 2024 bulk sender requirements mandate all three for high-volume senders. Even at lower volumes, missing any one of them creates a gap that inbox providers use to justify filtering your mail.
How often should I clean my email list?
At minimum, remove hard bounces immediately after they occur, most ESPs do this automatically. Beyond that, run a full validation pass before re-engaging a list segment that has not been mailed in six or more months, and suppress subscribers who have not opened in 90 to 180 days (after running a re-engagement sequence). The goal is a list where a high share of addresses are active and deliverable, because engagement signals are one of the strongest inputs into inbox placement decisions.
Does list size affect deliverability?
Not directly, but the relationship between list size and engagement quality does. A large list with low engagement produces poor open and click rates, which are negative reputation signals. A smaller, highly engaged list often has better inbox placement precisely because providers see consistent positive engagement signals. Growing your list without a parallel focus on list hygiene and engagement will eventually hurt deliverability.
What tools should I use to monitor email deliverability?
Google Postmaster Tools (free) is the most direct view into Gmail deliverability, showing domain reputation, spam rate, and authentication pass rates. Microsoft SNDS (free) provides equivalent visibility for Outlook. Litmus and Email on Acid are paid tools that show inbox placement across providers and email clients before you send. Your ESP's built-in analytics, open rate, bounce rate, unsubscribe rate, complaint rate, are the baseline to watch on every send.