15 ways to improve email deliverability and reach more inboxes

You wrote a good email. You sent it to people who signed up. And a large part of it never reached anyone.

This is the most frustrating problem in email marketing, because nothing looks broken. Your platform says the campaign was sent. Your report shows a number. But the number is lower than it should be, and you cannot see why.

The reason is that email providers do not just carry your message. They judge it first. They look at who you are, how your domain is set up, how clean your list is, and how people have reacted to you in the past. Then they decide.

This guide covers 15 things you can control. They are ordered roughly by impact, so if you only do the first five you will already be in better shape than most senders.

First: delivery is not the same as the inbox

These two words get mixed up constantly, and the difference matters.

Term	What it means	What your report shows
Delivery	The receiving server accepted your message.	“Delivered” or “Delivery rate”
Inbox placement	Where the message ended up after being accepted.	Usually nothing. Your platform cannot see this.

A 99 percent delivery rate does not mean 99 percent of people saw your email. It means the servers took it. The message could still be sitting in a spam folder.

Send to people who expect your emails

Everything else in this guide is easier if you get this one right. Deliverability is mostly a reputation system, and reputation comes from how people react to your messages.

If someone asked for your emails and remembers doing it, they open, they click, and they do not complain. If they did not ask, they mark you as spam. A handful of complaints can undo months of careful work.

Make sure people really signed up

• Tell people what they are signing up for. “Get our weekly tips” sets an expectation. “Subscribe” sets none.
• Do not pre-tick the consent box. Some countries do not allow it, and it produces subscribers who do not remember you.
• Consider double opt-in. You send one confirmation email, and only confirmed addresses join the list. You get fewer subscribers, and much better ones.
• Send a welcome email immediately. People are most engaged in the first hour. It also tells you straight away whether the address works.

Validate your list before sending

This is the fastest improvement available to most senders, and the one people skip most often.

Email list validation means checking whether each address actually exists before you send to it. A validation tool connects to the mail server for each domain and asks whether the mailbox is there. No email is sent during the check.

The reason this matters so much is simple. Dead addresses cause hard bounces, and hard bounces are the clearest signal to a provider that you do not check your list.

When to validate	Why
Before any large campaign	One bad send affects every campaign after it
Before mailing a list you have not used in six months	Email data is commonly estimated to decay by 20 to 30 percent a year
After importing a list from another system	Old exports often contain addresses already removed elsewhere
On a regular schedule	Monthly if you add contacts weekly, quarterly otherwise

What a good result looks like

A validation tool sorts your addresses into groups. Send to the valid ones. Remove the invalid ones. Keep the uncertain ones in a separate list rather than deleting them, because “uncertain” is not the same as “fake”.

We have two deeper guides if you want them: what email validation is and how it works, and a comparison of seven validation tools including what a year of each one costs.

Clean your list after every campaign

Validation before sending and cleaning after sending are two different jobs. You need both.

	Validation (before)	Cleaning (after)
When	Before the send	After each campaign
What it uses	A live check of each address	The results your campaign produced
What it catches	Addresses that do not exist yet unknown to you	Bounces, complaints, unsubscribes
Purpose	Prevent damage	Record what happened

After every send, do these four things

• Remove hard bounces immediately. The address does not exist. Sending again is the same mistake twice.
• Watch repeated soft bounces. One is normal. Four in a row means the mailbox is probably gone.
• Process unsubscribes fast. Someone who unsubscribes and gets another email will mark it as spam.
• Treat a complaint as a removal. If someone marks you as spam, take them off every list, not just the one they were on.

Focus on engaged subscribers

Providers watch how people react to you. Someone who never opens anything for a year is telling Gmail something about your email, and Gmail listens.

Sending to everyone on your list every time feels safe. It is not. A large inactive group quietly drags down the delivery of your whole campaign, including messages to people who do want them.

How to segment without guessing

Group	What to do
Active in the last 90 days	Send normally
No activity for 6 months	Reduce frequency, send your best content only
No activity for 12 months	Run one re-engagement campaign, then stop sending
Never opened anything, ever	Check the address is real, then let them go

Authenticate your sending domain

Authentication proves that you are allowed to send email using your domain name. Without it, providers cannot tell you apart from someone pretending to be you.

Since February 2024, Google and Yahoo require this. Microsoft added its own version in 2025. This is no longer optional.

Record	What it does	Required?
SPF	Lists which services are allowed to send email for your domain	Yes
DKIM	Adds a signature proving the message really came from you and was not changed	Yes
DMARC	Tells receiving servers what to do when a message fails the checks	Yes above about 5,000 messages a day

You can start DMARC with a policy of p=none. It changes nothing about how your mail is handled and only collects reports, which is enough to meet the requirement while you learn. The full official list is here: Google’s email sender guidelines.

Use a clear, consistent sender identity

People decide whether to open your email by looking at the sender name first. Providers watch that name too, and they build reputation around it.

Four rules that cost nothing

• Use a name people recognise. Your brand name, or a person at your brand. Not “Marketing Team” and not “noreply”.
• Send from your own domain. Never send bulk email from a free address like @gmail.com. Gmail treats that as impersonation.
• Use a reply address that works. A noreply@ address tells people you are not listening, and replies are a positive engagement signal you are throwing away.
• Stay consistent. Changing your sender name every campaign resets the recognition you built.

Separate your message types

Marketing email and important account email should not share the same sending address. If your promotions cause complaints, you do not want password resets caught in the same net.

Message type	Example sending address
Newsletters and offers	[email protected]
Receipts and invoices	[email protected]
Account and security	[email protected]

Choose the right email service

Your sending platform does more than press send. It handles the parts of deliverability that are hard to do yourself.

What a good platform must handle

• Bounce processing. It should stop sending to hard bounces automatically.
• Complaint feedback. When someone marks you as spam, the platform should receive that and remove them.
• Unsubscribe handling. Including one-click unsubscribe, which is now required for bulk marketing mail.
• Authentication support. It should give you SPF and DKIM records for your own domain.
• Sending rate control. So a large campaign goes out at a steady pace instead of all at once.

Increase your sending volume slowly

Providers are suspicious of sudden change. A domain that sends 200 emails a week and then sends 50,000 in one morning looks exactly like a compromised account.

This matters whenever something is new: a new domain, a new IP, a new platform, or a list you have not mailed in a long time.

A simple warm-up plan

Week	Send to	Who
1	Your most engaged 500	People who opened something in the last 30 days
2	Around 1,500	Active in the last 90 days
3	Around 5,000	Active in the last 6 months
4 and after	Increase by about half each week	Widen gradually

Watch your bounce and complaint rates at every step. If either rises, stop increasing and fix the cause before continuing. Google’s own advice is to send at a steady rate and avoid sudden spikes.

Control how often you send

There is no perfect sending frequency. There is only the frequency your subscribers expect.

If you promised a weekly newsletter, send weekly. If you suddenly send three times a week, people do not think “more value”. They think “too much” and reach for the spam button.

Watch for accidental overlap

This is the hidden problem. You have a newsletter. You also have an automated welcome sequence, an abandoned cart email, and a promotion running this week.

One person can receive all four in two days. Each one seemed reasonable on its own. Together they look like spam.

Make unsubscribing easy

This feels wrong to many marketers. It should not. An unsubscribe costs you one contact. A spam complaint costs you deliverability for everyone.

When the unsubscribe link is hidden, tiny, or broken, people do not give up. They click the spam button instead, because it is right there and it works.

Type	Where it appears	Required?
One-click unsubscribe	A link at the top of the message, added by the provider from a header in your email	Yes, for marketing mail above about 5,000 a day
Footer link	Inside your message, at the bottom	Always include one as well

One-click unsubscribe is a technical header your platform adds, defined in RFC 8058. Most modern platforms support it, but you may need to enable it. It does not replace your footer link. You need both.

Write honest subject lines

A misleading subject line can win you one open. It then costs you every open after that, because people learn not to trust you.

Spam filters read the gap between your subject line and your content. So do humans, and their reaction is what the filters measure.

Avoid these

• Fake replies and forwards. Starting a subject with “Re:” or “Fwd:” when it is neither. Google names this specifically.
• False urgency. “Last chance” every single week teaches people your deadlines are not real.
• ALL CAPS and rows of exclamation marks. They look like the spam people already recognise.
• Promises the email does not keep. If the subject says 50 percent off, the offer must be in the email.

Keep your design and links trustworthy

How your email is built affects whether it arrives, not just how it looks.

Design

• Never send an email that is one big image. Filters cannot read it, and many people have images turned off. They see a blank message.
• Keep a healthy balance of text. Real sentences, in real text, not inside pictures.
• Design for a phone first. Most people will read it on one.
• Watch the size. Gmail is widely reported to clip messages larger than about 102 KB, hiding the rest behind a “View entire message” link, including your unsubscribe footer. Google does not document a figure, so treat it as a practical limit rather than an exact one.

Links

• Link to your own domain where you can. Links to unfamiliar domains look worse.
• Avoid public link shorteners. Spammers use them to hide destinations, so filters treat them with suspicion.
• Check every link before sending. A broken or redirected link can trigger a filter.
• Do not attach files to marketing email. Link to them instead. Attachments raise suspicion and increase size.

Test the real email before launch

A preview inside your email platform is not a test. It does not go through your actual sending path, so it cannot show you what recipients will see.

Send the real campaign to yourself, through the same platform, from the same address.

What to check in that test message

• Authentication. Open “Show original” in Gmail and confirm SPF, DKIM and DMARC all say PASS.
• The sender name. Is it what you expected, on both phone and desktop?
• Every link. Click all of them, including the ones in the footer.
• The unsubscribe link. Actually use it on a test address and confirm it works.
• Personalisation. Look for empty gaps where a first name should be.
• Where it landed. Check Gmail, Outlook and one more provider if you can.
• Clipping. If Gmail shows “View entire message”, your email is too large.

Monitor more than open rates

Open rate is the number everyone looks at, and it is the least reliable one you have. Privacy features inflate it, image blocking hides it, and Google does not track it at all.

Metric	Healthy	Take action
Hard bounce rate	Under 1%	Above 2%
Total bounce rate	Under 2%	Above 5%
Spam complaint rate	Under 0.1%	Approaching 0.3%
Unsubscribe rate	Under 0.5%	Above 1%
Click rate	Varies by industry	Any sudden drop

Look at providers separately

Your overall numbers can hide a serious problem. If Gmail delivery collapses but Outlook is fine, the average still looks acceptable. Split your reporting by provider so you see it early.

Act fast when problems appear

Deliverability problems get worse while you wait. The provider is forming an opinion, and every campaign you send adds to it.

The moment you notice something wrong

1. Pause the affected sending. Not everything, just the segment or campaign showing the problem.
2. Read the actual error. Bounce messages contain a code and a sentence. They usually tell you the real cause.
3. Check what changed. New list, new template, new platform, higher volume? The cause is usually the most recent change.
4. Fix it, then restart small. Go back to your most engaged subscribers and build up again.

What you see	Usual cause
Sudden rise in hard bounces	An unvalidated or old list
550 5.7.1 rejections	Your sending IP has a poor reputation or is on a blocklist
5.7.26 errors	Authentication failing. Check SPF, DKIM and DMARC. See Google’s SMTP error reference
Messages deferred or slowed	Sending too fast, or volume increased too quickly
Gmail delivery drops, others fine	Check your spam rate in Postmaster Tools

Your pre-send checklist

Run through this before every campaign. It takes a few minutes.

• The list contains only people who signed up
• The list was validated recently, and invalid addresses were removed
• Hard bounces and complaints from the last campaign are removed
• Unsubscribes are synced across every system I use
• SPF, DKIM and DMARC show PASS on a real test email
• The sender name and reply address are correct and consistent
• The subject line matches what is actually inside
• The email is not one large image, and it is under 102 KB
• Every link works, including the unsubscribe link
• I sent a real test to Gmail and Outlook and checked where it landed
• Volume is similar to my recent sends, or increasing gradually
• I know which numbers I will check afterwards, and when

Frequently asked questions

Can I guarantee that every email reaches the inbox?

No, and nobody can. You control your list, your setup and your sending behaviour. The receiving provider makes the final decision, using signals you cannot see. Doing everything in this guide gives you the best possible chance, not a guarantee. Be careful with any service that promises one.

Is Gmail’s Promotions tab the same as spam?

No. Promotions is part of the inbox. People open it on purpose when they are looking for offers. Spam is a separate folder that most people never open. Landing in Promotions is normal for marketing email and is not a deliverability problem.

Does email validation prevent every bounce?

No. It removes addresses that do not exist, which is the largest cause of hard bounces. It cannot prevent a mailbox filling up, a server going down, or an address that closes the day after you checked it. Expect a big reduction, not zero.

Is a dedicated IP always better?

No. A dedicated IP starts with no reputation, and you have to build one with consistent volume. Below roughly 100,000 emails a month, a well managed shared IP usually performs better. Choose a dedicated IP when your volume is high and regular.

Does plain text always perform better than HTML?

No. HTML email is completely normal and delivers well when it is built properly. What causes problems is bad HTML: emails that are one large image, very heavy files, or messy code. A clean HTML email with real text is fine.

How long does it take to fix a damaged sender reputation?

Usually weeks, sometimes months. Reputation is built from a history of good sending, so the only way back is a period of clean, small, engaged sending. There is no fast reset, which is exactly why prevention is worth the effort.

Sources

The provider requirements and thresholds in this guide come from official documentation. These rules change, so check the originals before making decisions:

• Google — Email sender guidelines. Authentication requirements, the 5,000 per day threshold, spam rate limits, one-click unsubscribe, and sending practices.
• Google — Email sender guidelines FAQ. Updates and clarifications to the rules above.
• Google Postmaster Tools. Spam complaint rate, domain reputation and authentication reporting.
• Google — SMTP error reference. The meaning of bounce codes such as 550 5.7.1 and 5.7.26.
• Yahoo — Sender Best Practices. Reverse DNS requirements, complaint rate guidance, and separating bulk from transactional mail.
• RFC 8058. The technical standard behind one-click unsubscribe.

Figures without a link, such as typical list decay rates and healthy click rates, are widely used industry estimates rather than published standards. Treat them as guidance, and measure your own numbers wherever you can.

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We build MetaLogic MailVexa, so weigh our opinion of it accordingly. Everything else in this guide applies whichever tools you use. Provider requirements change, so check Google’s sender guidelines for the current rules.