Email deliverability

What it is and how to improve it

You can prepare a brilliant campaign and get zero results if nobody sees it. That is why email deliverability deserves as much attention as the subject line, the design or the offer.

This concept sounds technical, but it affects something very simple: the chance that your message shows up where the recipient can find it.

Short answer: what is deliverability?

Deliverability is the ability of an email to reach the recipient’s inbox. Good deliverability reduces rejections and keeps you out of the spam folder. It depends on authentication, sender reputation, list quality, content and user engagement.

Your sending platform has an influence, although no tool can promise perfect inbox placement. Providers such as Gmail or Outlook decide where each message goes.

Email delivery and deliverability: two different metrics

These terms are often used as synonyms. However, they describe different moments in an email’s journey.

The delivery rate shows how many messages the destination server accepted. An accepted email can end up in the primary tab, promotions or spam.

Deliverability, on the other hand, focuses on reaching the inbox. Therefore, a high delivery rate does not guarantee good visibility.

Imagine you send 10,000 emails. The servers accept 9,800, but 2,000 end up in spam. Delivery reaches 98%, although inbox placement is considerably lower.

This difference prevents wrong diagnoses. If you only look at bounces, you might think everything is working fine.

How to calculate the deliverability rate

The most useful formula to estimate it is this: emails that reach the inbox ÷ emails delivered × 100.

The problem lies in the numerator. Email marketing tools know about acceptances and bounces, but they don’t always receive the exact location of each message.

That is why the deliverability rate is usually estimated with placement tests and complementary signals. It is worth reviewing opens, clicks, bounces, complaints and errors by provider.

A drop in opens does not prove a deliverability problem by itself. It may be due to a weak subject line, a barely relevant offer or privacy changes.

Look for several signals pointing in the same direction. Analyzing them together gives a much more reliable picture.

What counts as good email deliverability

There is no universal percentage that guarantees results. The figure changes depending on the industry, the country, the email provider and the quality of the audience.

As a guideline, a delivery rate below 95% deserves an immediate review. For inbox placement, the closer you get to 100%, the better.

Compare each campaign with your own history. Also separate the results for Gmail, Outlook, Yahoo and corporate domains.

An overall average can hide a major block. Your emails may reach Gmail well but suffer rejections at Outlook.

If you are looking for local context, check out our analysis of email marketing deliverability in Spain.

The factors that most affect deliverability

Filters don’t assess a single element. They combine technical, historical and behavioral signals to calculate the risk of each send.

Sender domain authentication

SPF, DKIM and DMARC help prove that you are allowed to send messages from your domain. They also reduce the risk of spoofing.

SPF declares which servers are authorized to send on behalf of your domain.
DKIM adds a signature that makes it possible to verify the authenticity and integrity of the message.
DMARC defines how to handle failures and requires alignment with the sender’s visible domain.

Gmail bulk senders must use SPF, DKIM and DMARC. In addition, the domain in the “From” field must be aligned with SPF or DKIM.

In this guide to setting up SPF, DKIM, DMARC and a custom domain we explain each setting.

Domain and IP reputation

Every send leaves a history. Providers look at complaints, bounces, volume, authentication and recipient engagement.

A good reputation opens doors. A poor reputation increases rejections and the likelihood of landing in spam.

The domain represents your brand. The IP identifies the infrastructure that transmits the messages. Both elements can influence deliverability.

Quality and origin of your database

A big list is not always a valuable list. Old addresses, purchased ones or ones collected without permission generate more bounces and complaints.

They may also contain spamtraps. These trap addresses make it possible to detect poor collection or maintenance practices.

Double opt-in confirms that the address exists and that the person wants to receive your emails. It also creates a positive first interaction.

Recipient engagement

Providers learn from the behavior of their users. Opens, clicks, replies and moves out of spam can signal interest.

Constant deletions, lack of activity and complaints send the opposite signal. That is why segmenting improves relevance and deliverability.

Don’t send every campaign to your whole list out of habit. Select the people who have a real interest in the topic.

Sending volume and frequency

Sudden changes raise suspicion. A new domain that jumps from one hundred to one hundred thousand messages lacks enough history.

Warming up means increasing the volume gradually. Start with active contacts and expand the group if the metrics respond well.

After that, keep a reasonably steady cadence. Long absences followed by big sends tend to harm email deliverability.

Email content, links and design

Content matters, although the old “forbidden words” lists oversimplify the problem. Context weighs more than an isolated word.

Watch out for exaggerated promises, link shorteners, suspicious links and faulty HTML code. Also avoid building the whole message as a single image.

A clean design makes reading easier and reduces errors. You can learn more about this point in our glossary entry on antispam filters.

Unsubscribes and spam complaints

A simple unsubscribe process protects your reputation. When someone can’t find that option, they may mark the email as spam.

Gmail asks bulk senders to offer one-click unsubscribe in promotional messages. Requests must be processed quickly.

Gmail also recommends keeping complaints below 0.1% and preventing them from reaching 0.3%. Even a small percentage is already a serious signal.

How to know if you have a deliverability problem

A sudden drop needs context. Before changing everything, identify when it started and what changed on that date.

Observed signal	Likely cause	First check
Hard bounces increase	Invalid addresses or an old list	Review the origin and collection date
Opens drop at one provider	Filtering or provider-specific reputation	Split metrics by receiving domain
Temporary rejections appear	Sudden volume or low reputation	Read the SMTP codes and review your cadence
Complaints rise	Lack of recognition or relevance	Review permission, frequency and segmentation
Emails land in spam	Authentication, reputation or content	Check SPF, DKIM, DMARC and the message
Campaigns fail after switching platforms	Incomplete setup or new volume	Validate DNS and warm up the domain

Error codes provide more precise clues than a general impression. A rejection due to authentication requires a different fix than a nonexistent mailbox.

Google Postmaster Tools also lets you monitor reputation, authentication, errors and spam for Gmail. Compare that data with the reports from your platform.

How to improve deliverability step by step

Start with the problem that has the biggest impact. Changing colors or subject lines will do little good if your domain is not authenticated.

Authenticate your domain with SPF, DKIM and DMARC, and check its alignment.
Confirm permission and remove any purchased list or list of doubtful origin.
Clean your list to stop sending to hard bounces and to contacts with prolonged inactivity.
Segment by interest and prioritize the people who engage with your brand.
Stabilize your volume and warm up new or inactive domains gradually.
Make unsubscribing easy and process requests without friction.
Review your content to spot problematic links, HTML errors and unbalanced designs.
Measure by provider and document every change to know which action produces improvements.

Make one significant change at a time whenever possible. If you change the domain, the list, the content and the frequency all together, you will lose the ability to diagnose.

What to do if deliverability suddenly drops

First, pause the least important sends. Continuing to push can prolong the damage, especially if complaints or bounces are rising.

Then, review the SMTP codes, authentication and recent changes. Also check whether your domain or IP appears on an email blacklist.

Send your next campaigns to the most active segment. Reduce the volume and get back to a steady cadence while you watch the response by provider.

Don’t delete your whole list without analyzing it. Separate active, inactive, bounced and never-engaged contacts. Each group needs different treatment.

Recovery rarely happens within hours. Filters need to receive new, consistent signals before updating their assessment.

Common mistakes that hurt deliverability

Buying a database is usually the most expensive mistake. It offers immediate volume, but lacks permission, context and a prior relationship.

Another common mistake is hiding the unsubscribe link. That friction turns a normal exit into a spam report.

Using a free sender address for business campaigns also hurts. Your own domain lets you authenticate your identity and build brand reputation.

Sending only when you need to sell produces spikes and fatigue. Useful, steady communication generates better signals in the long run.

Finally, avoid becoming obsessed with a supposed magic word. Deliverability depends on a system of signals, not on isolated tricks.

How Mailrelay helps improve deliverability

The platform does not replace a good permission strategy. However, reliable infrastructure and clear tools make day-to-day work easier.

With Mailrelay you can create campaigns, manage contacts, segment audiences and check statistics in real time. You also have essential automations and A/B tests.

Our dashboard lets you check your email authentication. That way you can spot pending setups before launching an important campaign.

We also manage bounces, unsubscribes and complaints to help you keep your list in better shape. The reports show the response to each send, along with click maps.

The editor generates proper HTML and offers an antispam report. It also includes AI writing assistance to prepare subject lines and content.

We have our own infrastructure and IP ranges under our control. This helps us take care of the quality of the sending environment.

If you need help, our expert, multilingual support team is available even on the free account. We can help you with setup and deliverability questions.

You can also start with up to 80,000 emails per month and 20,000 contacts. That makes it easier to test, measure and improve without taking on an upfront cost.

Deliverability in marketing and transactional emails

Both types of message go through similar filters, but they serve different purposes. A newsletter can wait; a password reset is usually urgent.

It is worth separating the flows when the volume justifies it. That way, a problem with promotional campaigns will have less impact on critical messages.

Keep identity, authentication and tracking consistent in both cases. Also monitor the deliverability of confirmations, invoices and automated notices.

Our article on the deliverability of confirmation emails goes deeper into that first contact.

Frequently asked questions about deliverability

These answers address the questions that usually come up before sending a campaign or during a delivery problem.

Why do my emails land in spam?

The most common causes are incomplete authentication, poor reputation, complaints, lack of engagement or old lists. Irregular volume, links and content also play a part. Review the delivery codes and segment the data by provider before drawing conclusions.

Are deliverability and delivery rate the same thing?

No. The delivery rate measures the messages accepted by the receiving server. Deliverability estimates how many of them reach the inbox. An accepted email can end up in spam, so both metrics should be analyzed together.

Do SPF, DKIM and DMARC guarantee reaching the inbox?

They don’t offer a guarantee. These protocols authenticate the origin and help protect your domain. Providers also weigh reputation, complaints, volume and recipient engagement.

What bounce rate is acceptable?

The lower, the better. A rate above 2% usually justifies a review of the list and its origin. Hard bounces should stop receiving emails, because they correspond to invalid or nonexistent addresses.

Does a dedicated IP always improve deliverability?

Not always. A dedicated IP offers more control, but it also requires enough volume and constant management. With low traffic, quality shared infrastructure can be more stable.

Should I remove all inactive subscribers?

First define what “inactive” means for your purchase cycle. Then try a reactivation campaign. If there is no response, excluding those contacts usually protects costs and reputation.

How long does it take for a domain’s reputation to recover?

It depends on the severity and the history. An improvement can take days or several weeks. Fix the cause, reduce the volume and send consistently to active contacts.

Does switching platforms fix poor deliverability?

Only when the previous infrastructure was part of the problem. If you keep a poor list, high complaints or a badly authenticated domain, you will just carry the problem over. Audit your data, setup and strategy first.

Do words like “free” make an email go to spam?

An isolated word rarely decides the fate of a message. Filters evaluate many signals. Avoid misleading promises and combine clear content with good reputation, permission and authentication.

How can I test deliverability before sending?

Check SPF, DKIM and DMARC, review the antispam report and send tests to several providers. For sensitive campaigns, use an inbox placement test. Then validate the real result with reports, SMTP codes and reputation data.

Deliverability is built with every send

Reaching the inbox takes technique, permission and consistency. A single campaign can go well, but reputation is shaped by the full history.

Authenticate your domain, take care of your list and send content people expect. Also make unsubscribing easy and analyze each provider separately.

At Mailrelay we bring together the tools and support needed to put these practices into action. You can create your free account and start improving with real data.

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