Email deliverability is never done

You’ve put time into the copy, debated the subject line and checked every link. You hit send, and the report says “delivered”.

Lovely. But did it reach the inbox?

I joined a session with ZeroBounce at HubSpot UNBOUND, and one message really stuck with me: a clean list today doesn’t stay clean on its own.

People change jobs. Email addresses stop working. Typos sneak through forms. Bots do their thing. Your database keeps changing, and your sending reputation changes with it.

I pulled together the key learnings and actions below because this deserves more than a page of conference notes that never gets opened again. There are some straightforward things we can all do to give our emails a better chance of being seen.

The numbers worth keeping an eye on

Before changing anything, get a feel for where you stand. These are useful starting points for reviewing your email health:

• Hard bounces: Under 1%
• Total bounces: Under 2%
• Authentication: SPF · DKIM · DMARC
• Engagement windows: 0-90 / 90-180 / 180+ days
• Maintenance: Weekly · Monthly · Quarterly, with an owner

These aren’t magic numbers that guarantee inbox placement. They give you a baseline and help you spot when something needs attention.

How bad data becomes a bigger problem

An old email address doesn’t look particularly threatening sitting in your CRM.

Multiply it by hundreds or thousands, keep sending to it, and the picture changes.

What builds up: Risky contacts

• Invalid addresses create bounces
• Disposable addresses may expire soon after sign-up
• Spam traps can expose poor collection or maintenance
• Catch-all domains accept mail without confirming the mailbox exists

What follows: Reputation damage

• Bounces climb
• Spam complaints climb
• Providers block or throttle sends
• Good contacts land in spam too

They need different treatment, but they all deserve attention before a major send.

Poor list health can affect more than the contacts causing the problem. As your sending reputation suffers, emails to people who actually want to hear from you can end up in spam too.

That’s a frustrating outcome after all the work that went into the campaign.

An unsubscribe isn’t a failure

It’s tempting to treat every unsubscribe as a loss. But someone telling you they no longer want your emails is useful information.

Make it easy for them to leave, and respect that choice.

A spam complaint is a much less friendly way of delivering the same message.

Show email providers you’re legitimate

SPF, DKIM and DMARC. Three acronyms that are very easy to leave with “the technical person”.

You don’t need to become a DNS expert, but you do need to know whether these foundations are working.

• SPF (who can send): Identifies which services are authorised to send using your envelope-sender domain.
• DKIM (signature): Adds a digital signature that helps receiving servers verify the signing domain and detect changes to the message.
• DMARC (policy): Checks whether the domain people see in your From address aligns with a passing SPF or DKIM result. It also publishes your policy for messages that fail.
• Alignment (verification): The connection between your visible From domain and the domain authenticated by SPF or DKIM. Both don’t have to align for DMARC to pass.

If you’ve added a new sending platform, changed domains or inherited an existing setup, this is worth checking. Having records in place and having authentication working correctly aren’t always the same thing.

Look beyond “delivered”

A delivered email has been accepted by the recipient’s mail server. That doesn’t tell you which folder it reached.

Inbox placement testing, often called seed testing, sends your campaign to test accounts across providers such as Gmail and Outlook. It gives you a useful view of where those test messages land, although individual subscribers may see different results.

• Inbox. Where you want to be. Measure campaigns against this, not the delivery rate, which counts spam-folder placement as “delivered”.
• Spam. If test messages are landing here, there’s a reputation or setup issue worth fixing before the next send.
• Opens and clicks. Only meaningful once you know the email reached the inbox in the first place.

If your emails are being delivered but engagement has dropped, inbox placement is one of the things worth investigating.

Otherwise, you could spend weeks tweaking content when part of the problem happens before anyone sees it.

Your most engaged contacts deserve a different approach

Someone who clicked your last campaign and someone who hasn’t interacted with your emails for a year shouldn’t automatically receive the same treatment.

Reviewing engagement in windows can help:

• 0-90 days, engaged: Your recently active audience.
• 90-180 days, warm: Review relevance, frequency and opportunities to reconnect.
• 180+ days, cold: Make a deliberate decision about re-engagement or suppression.

Adjust these windows to how often you send and how your customers buy. Use clicks and other meaningful activity alongside opens.

Prioritising engaged contacts can be part of a sensible sending approach. But a delay of a few hours won’t make an inactive audience more interested. The important decision is whether they should receive that campaign at all.

Six quick wins you can make this week

There’s plenty to think about here, but you don’t have to turn it into a six-month project. Start with these.

1. Authenticate your domain. Check SPF, DKIM and DMARC across the platforms sending your emails. Confirm they’re working, rather than assuming someone sorted it years ago.
2. Suppress hard bounces. Make sure addresses returning permanent failures are excluded from future marketing sends. You can retain the CRM record without continuing to email it.
3. Validate new contacts. Catch invalid and mistyped addresses before they become part of a campaign. Forms, imports and integrations all deserve a look.
4. Suppress known risks. Keep unsubscribes, known complainers and invalid addresses out of your marketing sends. Review other validation risks before deciding how to handle them.
5. Prioritise engaged subscribers. Build your campaigns around people who are actively interacting with your business. Have a separate plan for contacts who have gone quiet.
6. Monitor inbox placement. Look beyond the delivery percentage. If there are signs of a problem, investigate where your messages are landing.

Pick one, give it an owner and get it moving. Then tackle the next.

The 30-minute inbox protection check

This is the part I’d encourage you to actually put in the calendar.

Set aside half an hour, open your CRM and recent campaign reports, and work through these five checks. You’re looking for gaps and deciding what needs attention first.

1. Validate list health: Where are contacts coming from? Are addresses checked before you send? Review invalid addresses, typos, disposable addresses and other validation risks.
2. Review reputation signals: Look at bounces, complaints and blocks across recent campaigns. Check for patterns by audience or contact source, rather than looking at the overall average alone.
3. Confirm authentication: Check SPF, DKIM, DMARC and alignment for the services sending on your behalf. Include any tools or domains added since the last review.
4. Check inbox placement: Review recent seed tests and any reports of emails landing in spam. If testing isn’t set up, assign someone to organise it.
5. Review engagement: Check who is still receiving your campaigns despite a long period of inactivity. Confirm that you have a clear approach to re-engagement and suppression.

You may uncover work that takes longer than half an hour. That’s fine. The aim is to leave with clear priorities, an owner and a next step.

Your deliverability scorecard

How many of these can your team confidently tick?

Tick what’s true today: 8 checks for a healthy list

List health

• Hard bounce rate is under 1%.
• Total bounce rate is under 2%.
• Spam complaints are monitored, and complainants are suppressed.
• Validation results are reviewed before major sends.

Sending health

• SPF, DKIM and DMARC are correctly configured and working.
• Inbox placement is tested across major providers.
• Engaged subscribers are prioritised for important campaigns.
• A recurring list maintenance routine has an owner.

Note: If three or more boxes are left unticked, start there before increasing your sending volume.

Give it a routine

A one-off clean-up helps. Then more contacts arrive, more people change jobs, and the list keeps moving.

A simple routine makes the work easier to maintain.

Weekly

• Review bounce and complaint spikes
• Suppress newly identified risks
• Investigate unusual campaign results

Monthly

• Check fast-growing lists and new contact sources
• Review engagement by provider where available
• Update suppression rules

Quarterly

• Review database health, authentication and sending domains
• Review your approach to inactive contacts
• Use your findings to decide where further validation is needed

The most useful question here might be: whose job is this?

If nobody owns it, it’s very easy for “we should check that” to become something you revisit after a campaign goes wrong.

Stop bad data at the door

Once you’ve dealt with the immediate gaps, look at what you can automate.

• Address validation: on your forms
• Bot protection: keep fake sign-ups out
• Suppression rules: exclude known risks
• Scheduled checks: paced to how your list grows

These are practical ways to reduce the amount of manual clean-up your team needs to do later.

Remember: Validation checks the address. It doesn’t establish permission to send marketing emails.

Three questions to take back to your team

What are we optimising for?

A bigger mailing list can look impressive in a report. What matters is whether you’re reaching people who want to hear from you and helping them take a useful next step.

What’s our baseline?

Before setting targets, understand your current bounce rates, complaints, authentication and inbox placement. You need something meaningful to compare against.

Who owns the routine?

Whether it sits with your internal team or with us, give someone responsibility for keeping it moving.

Let’s protect the list

My biggest takeaway from the ZeroBounce session was that deliverability needs to be part of how we run email marketing, alongside the content, design and reporting.

It deserves regular attention, and a little structure makes that much easier. Start with the 30-minute check. See what you find.

Want us to work through it with you? Get in touch with BLOOM. We’ll help you identify what needs attention and put a practical plan around it.