Why Is Your Email Going Into Spam? How to Boost Deliverability in 2026

Quick answer: Emails usually land in spam for one of six reasons: the sending domain is not authenticated, the unsubscribe process is unclear, the spam-complaint rate is too high, the sender reputation is low, the content trips spam filters, or the list is full of stale, unengaged contacts. The most important fix is authentication: since 2024 Google, Yahoo and (from May 2025) Microsoft require bulk senders to set up SPF, DKIM and DMARC, offer one-click unsubscribe, and keep spam complaints below 0.3%. Get those right, keep your list clean, and warm up new sending accounts gradually, and your deliverability will improve.

Ever wonder why some emails land in the inbox like a trusty paper plane, while others plummet straight into the spam folder? It comes down to strategy, timing and a bit of technical housekeeping. Whether you are launching a shiny new campaign or reviving an old sending account, getting your emails seen, and not just sent, is what really counts.

In this guide we dive into how to make sure your emails reach their intended destination, from authenticating your domain to warming up a new sending account. And the rules have changed since we first published this post. Google and Yahoo tightened their sender requirements in 2024, and Microsoft followed in 2025, so the bar for reaching the inbox is now higher, and more strictly enforced, than ever.

The payoff for getting it right is real. Compliant senders average 89% inbox placement in 2026, while non-compliant senders see between 22% and 34% of their email routed to spam. Ready to leave the spam folder in the dust? Let’s get started.

Possible reasons why your emails are going into spam

Most spam-folder problems trace back to five root causes: missing authentication, a hard-to-find unsubscribe option, a high spam-complaint rate, a low sender reputation, or content that trips spam filters. Here is how each one works, and how to tell which is affecting you.

Unauthenticated emails

This is the big one, and it is no longer optional. Google and Yahoo began requiring email authentication for bulk senders in February 2024, and Microsoft introduced its own equivalent rules for Outlook, Hotmail and Live addresses from 5 May 2025. If your emails are not properly authenticated, you may find them delayed, sent to spam, or rejected outright. More on exactly what to set up below.

Unclear opt-out process

Google, Yahoo and Microsoft all now expect a simple, one-click way for recipients to opt out of your marketing emails, and they expect those requests to be honoured quickly. Bury the unsubscribe or drag your feet on processing it, and you invite the spam complaints that damage your deliverability.

High level of spam complaints

If your spam complaint rate creeps towards 0.3% or higher, expect delivery problems, from delays to spam placement to outright bounces. Google’s own guidance is to keep your reported spam rate below 0.1% and to avoid ever reaching 0.3%. Cross that line and Google will withhold delivery mitigation until you stay below 0.3% for seven consecutive days, so this is a threshold worth guarding carefully.

Neutral or low sender reputation

Your sender reputation is shaped by how recipients interact with your emails: opens, clicks and, unfortunately, spam complaints. A high bounce rate drags it down too, since emails that never arrive cannot engage anyone. Positive engagement does the reverse, steadily building both your reputation and your deliverability.

When you first set up a sending account, it has a neutral reputation. From then on, every action you and your recipients take is scored. Normal, everyday activity, such as sending and receiving a healthy volume of wanted email, builds a positive reputation. Bombarding inboxes with mail that gets ignored or flagged does the opposite, and quickly. Once your reputation dips below a certain threshold, mailbox providers like Gmail, Yahoo and Outlook may start blocking your messages altogether.

How to prevent your email from going into spam

Landing in the inbox rather than the spam folder takes more than luck. With the right approach you can dramatically improve your chances. Tools like Sender Score, Mailtrap and MXToolBox are invaluable for diagnosing deliverability issues by assessing your sending domain’s reputation. Once you have pinpointed the problem areas, you can put the fixes below in place.

1. Complete email authentication

Email authentication is a set of DNS records, SPF, DKIM and DMARC, that prove the emails you send genuinely come from you and not from an imposter spoofing your identity. It is the single most important thing you can do for your deliverability, and since 2024 it has moved from best practice to hard requirement.

The new baseline: what Google, Yahoo and Microsoft now require

All three major mailbox providers now enforce the same core trio of authentication protocols. The requirements are strictest for bulk senders, generally defined as anyone sending more than 5,000 emails per day to a given provider’s addresses, but the reality is that authentication now benefits every sender, and all three providers recommend it regardless of volume.

Here is how the current rules stack up across the three providers:

A crucial point for anyone using a marketing platform: these rules apply even if you outsource your sending to a third-party provider. Authentication is tied to your domain, so SPF, DKIM and DMARC have to be configured in your own DNS regardless of whether the mail physically leaves HubSpot, Mailchimp, Klaviyo or your own server.

The three pillars of standard email authentication are:

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

Together they confirm your identity as a sender, thwart spoofing and phishing, and bolster the overall security and deliverability of your mail. The guides below outline the steps for HubSpot users, but the process is very similar across platforms, and your provider’s knowledge base will have an equivalent walkthrough.

DKIM authentication

DKIM acts as a guardian that stops spammers from impersonating a legitimate domain. Most mailbox providers now require DKIM to confirm an email genuinely originates from an authorised sender on your domain. Mail lacking DKIM is far more likely to be rejected, quarantined or marked as spam. Quarantined emails can even show as delivered while remaining invisible to the recipient, which makes DKIM setup a wise move.

To set up DKIM in HubSpot:

1. Log into your hosting provider, domain registrar or DNS provider and open your DNS record settings.
2. You will typically add DKIM as a TXT record, though some platforms, HubSpot included, require two CNAME records instead.
3. Copy the Host (Name) and Required Data (Target) values provided and paste them into the corresponding fields in your DNS settings.

SPF authentication

Think of an SPF record as the guest list for your domain’s party. If a sender’s IP address or domain is not on the list, SPF acts like a bouncer stopping them at the door. It ensures only mail servers authorised to send on your behalf can do so. One thing to watch: SPF has a hard limit of 10 DNS lookups, and exceeding it causes SPF to fail silently, so keep your include chain lean or use a flattening tool if it grows long.

To set up SPF in HubSpot:

1. Log into your DNS provider and open your DNS record settings.
2. Search for an existing SPF TXT record, or create one if none exists.
3. If you are editing an existing record, modify it to include your provider’s details, for example: v=spf1 include:anotherprovider.com include:123456.spf03.hubspotemail.net -all
4. If you have no existing SPF record, create a new one using the Host (Name) and Required Data (Target) values provided.

DMARC authentication

DMARC builds on the foundations set by SPF and DKIM, adding a further layer of protection. It tells mailbox providers how to handle mail that fails SPF or DKIM checks, and it provides reports that help you spot authentication problems. Under the current rules you need a published DMARC policy of at least p=none, aligned with either SPF or DKIM, and preferably both.

To set up a DMARC policy in HubSpot:

1. Create a DNS TXT record that defines your DMARC policy.
2. Decide how to handle mail that fails checks, whether to reject it, quarantine it, or take no action. For example, p=none means no action is taken against unauthenticated mail, but you still receive reporting.
3. Optionally, add properties to specify whether and where authentication reports should be sent. HubSpot’s guide to DMARC covers these in detail.

A quick word on how seriously Microsoft is taking this. Rather than quietly routing non-compliant mail to junk, Outlook rejects it outright with a 550 5.7.515 access-denied error. The message simply never arrives. So authentication has become the price of entry to the inbox.

2. Make it easy to unsubscribe

Gmail, Yahoo and Outlook now expect senders to offer a genuine one-click unsubscribe, delivered through a list-unsubscribe header (the technical standard is RFC 8058), alongside a clearly visible unsubscribe link in the email body. Requests must be processed swiftly, within two days. No one should have to fight to stop receiving mail they no longer want, and making it hard is a fast route to spam complaints.

3. Monitor spam complaints

Keeping an eye on your complaint rate is essential for a healthy sending programme. Your email platform usually surfaces these figures in its campaign spam reports, though Gmail complaints can be trickier to track because of its privacy-protecting feedback loop.

To monitor Gmail complaints, link your domain to Google Postmaster Tools. It needs you to send at least 100 emails a day to Gmail accounts to gather meaningful data, and in return gives you a clear view of your spam rates, domain reputation and delivery errors. Its Compliance Status dashboard also shows, in real time, how you measure up against the current sender requirements.

4. Send wanted email

Email that is genuinely wanted and relevant improves the recipient’s experience and sharply reduces spam complaints. Keep your complaint rate below 0.3%, and ideally under 0.1%. Here is how to make sure your mail is welcome.

Respect unsubscribe requests

One of the quickest ways to trigger complaints is to keep emailing someone who has opted out. When a contact leaves your list, remove them promptly and take care to prevent accidental re-subscription. It respects their choice and keeps your list clean.

Set clear expectations

Tell subscribers what they are signing up for, the kind of content they will receive and how often, then stick to it. If someone signs up for a monthly newsletter, surprise weekly blasts are a recipe for dissatisfaction and complaints.

Personalise your communication

Personalisation lifts both relevance and reception. Addressing recipients by name and tailoring content to their interests shows you value the relationship, and makes your mail far more likely to be welcomed.

Send relevant content

Every email should serve the recipient’s interests and needs. Relevant content boosts engagement and minimises complaints, because people rarely report mail they find useful.

Avoid sending to unengaged contacts

As a rule, only send to contacts who have engaged within the last twelve months. Many platforms flag unengaged contacts for you. HubSpot, for instance, has a graymail suppression feature that automatically excludes them, categorising a contact as unengaged if they:

• Never engaged with your marketing email and have not engaged with your last 11 sends, or
• Previously engaged but have not engaged with your last 16 sends.

5. Create quality content

Standout content matters more than ever if you want your emails to resonate and to earn engagement. Here is how to craft mail that reaches the inbox and inspires action.

Optimise for mobile

With so many people reading on their phones, design for mobile first. Optimise layouts for smaller screens and test across devices to make sure everything displays as intended.

Right-size your images

Oversized images slow load times and can tip your emails towards the spam folder, so compress and correctly size every image before you send. We have a full companion guide on this, covering file sizes, formats and 2x retina images: email image size best practices. And for every image you include, add descriptive alt text, both for accessibility and because it gives filters helpful context when images are blocked.

Understand your audience

To write content that lands, you first need to understand your readers. Data enrichment tools like ZoomInfo can give you insight into your contacts’ professional backgrounds and interests, so you can tailor your messaging more effectively.

Segment your audience

Segmentation lets you deliver personalised experiences at scale. Divide your lists by criteria like demographics, engagement history or purchase behaviour so each subscriber gets content tailored to them, and consider dynamic content to personalise further within a single send.

Use AI thoughtfully

AI is now woven through the best email programmes, and used well it lifts both relevance and performance. Predictive send-time optimisation schedules each email for when a given contact is most likely to open, subject-line tools test and refine your wording, and generative AI speeds up drafting and dynamic content. One caveat: AI-generated copy still needs a human editorial pass, because spammy, generic or error-strewn content is exactly what filters and readers punish. Let it assist your writing, but keep a person in charge of it.

Avoid spam triggers

Steer clear of the classic red flags. Go easy on exclamation marks and avoid all-caps in subject lines and body copy. Words like “free”, “guarantee” and “buy now” can raise filter suspicion. Minimise attachments, keep your image-to-text balance sensible, and make sure real, meaningful text carries your message rather than a single large image.

6. Improve your sender reputation

A strong sender reputation is what keeps your mail landing in the inbox over the long term. Here is how to build and protect it.

Verify email addresses

Making sure the addresses you collect are valid reduces your bounce rate and lifts deliverability. You can verify manually by switching on double opt-in, where new subscribers confirm via a follow-up email, which also filters out fake or mistyped addresses. For a lighter-touch approach, tools like NeverBounce and ZeroBounce offer real-time and bulk verification to keep your list clean.

Combat list decay

Over time addresses go stale, pushing up bounce rates and dragging down engagement. Regular list cleaning is ongoing maintenance with long-term payoff: better deliverability, higher engagement and a stronger reputation. Verification and enrichment tools help, as does automatically removing unengaged subscribers.

Warm up your email sending

If you are starting with a new sending account, or reviving a dormant one, warming up is essential for building reputation, and for repairing it if it has taken a hit. The process means gradually increasing your sending volume over a few weeks, starting small and building up. It helps enormously if recipients open, reply to and mark these early emails as important, and move any that land in spam back to the inbox.

You can warm up manually by emailing accounts you own, or asking colleagues across different mailbox providers to interact with your sends. Automated tools like Warmy and Instantly streamline it using pools of real accounts to simulate genuine engagement. For a new account, expect the warm-up to run two to four weeks, with your inbox placement score climbing steadily as you go.

Final words

And there you have it, your toolkit for dodging spam filters and landing where you belong. The rules have tightened, and with Google, Yahoo and Microsoft now enforcing authentication, the cost of getting it wrong has never been higher. But the flip side is just as real: get the fundamentals right and you are set for stronger deliverability, higher open rates and better engagement.

Maintaining a great sender reputation is a bit like tending a garden. It takes regular care and attention. Put these practices in place, keep adapting, and your email marketing will thrive.

Boost your email performance

Need a hand getting your authentication, deliverability or wider email strategy in order? Reach out to Cybersolve for an email marketing consultation.