Most businesses don't know they have a deliverability problem until their open rates have been quietly tanking for months. By then, the damage to their sender reputation is real and fixing it takes time.
Email deliverability isn't glamorous. It sits under the surface of everything you do in email marketing, and when it's working, you don't notice it. When it breaks, nothing else you do matters - because your emails are going to spam before anyone has the chance to read them.
#What you'll learn in this post
- What email deliverability actually means
- Why emails end up in spam (and what's really behind it)
- How domain authentication works and why you need it
- The role of list hygiene in protecting your sender reputation
- How to diagnose and fix a deliverability problem
#What email deliverability actually means
Deliverability is the likelihood that your email lands in the recipient's inbox rather than their spam folder - or getting blocked entirely before it arrives.
It's not just about avoiding the word "free" in your subject line. That's 2004 thinking. Modern spam filters are sophisticated. They're looking at your sender reputation, your domain authentication records, your engagement rates, your sending patterns, and the technical setup of your sending infrastructure - all at once.
The two key numbers to watch are:
Inbox placement rate - what percentage of your sent emails actually reach the inbox (not spam). Most email platforms only show you what was "delivered," which means it reached the mail server. It doesn't mean it reached the inbox. Inbox placement is the harder number to get, but it's the one that matters.
Sender reputation - a score (or set of signals) that internet service providers and inbox providers use to decide how to treat your email. It's built up over time and can be damaged quickly by high bounce rates, spam complaints, or sudden spikes in sending volume.
#Domain authentication: the non-negotiable foundation
If you take one thing from this post, make it this: your sending domain needs to be properly authenticated before anything else matters.
There are three records you need to have in place. These aren't optional extras or advanced settings - they're the records that tell the world your email is actually from you, and without them, inbox providers have no reason to trust you.
SPF (Sender Policy Framework) is a DNS record that tells receiving mail servers which servers are authorised to send email on behalf of your domain. If an email claiming to be from your domain comes from a server not on your SPF list, it fails the check and is treated with suspicion.
DKIM (DomainKeys Identified Mail) is a cryptographic signature attached to every email you send. The receiving server checks the signature against a public key in your DNS records to verify the email hasn't been tampered with and genuinely came from you. Most email platforms generate your DKIM key for you - you just need to add the DNS record they provide.
DMARC (Domain-based Message Authentication, Reporting and Conformance) is the policy layer that sits on top of SPF and DKIM. It tells receiving servers what to do if an email fails authentication: quarantine it, reject it, or do nothing. It also enables reporting, so you can see what's being sent from your domain.
Most accounts we audit are missing DMARC entirely. SPF and DKIM are set, deliverability looks okay on the surface, but there's no policy layer and no reporting. You're flying blind.
In 2024, Google and Yahoo both tightened their requirements for bulk senders. SPF, DKIM, and DMARC are now effectively mandatory for anyone sending significant email volume to Gmail and Yahoo addresses. If you're not set up, you're already fighting a headwind.
Setting these records up requires access to your domain's DNS settings (usually through your domain registrar or hosting provider). Your email platform should tell you exactly what records to add - this is now standard in any reputable tool's setup guide.
#List hygiene: what it is and why it matters
Your sender reputation is partly determined by how your recipients behave when they receive your email. High open rates and clicks signal that people want to hear from you. High bounce rates and spam complaints signal that they don't - or that your list is dirty.
Hard bounces happen when an email is sent to an address that doesn't exist. A hard-bounced address should be removed from your list immediately. Most email platforms do this automatically now, but it's worth checking. A bounce rate above 2% will start to hurt your reputation.
Spam complaints are when someone marks your email as spam. ISPs watch complaint rates closely. A complaint rate above 0.1% (that's one complaint per 1,000 emails) starts to cause problems. Above 0.3% and you're in real trouble. The main ways to keep complaints down: only send to people who opted in, make unsubscribing easy, and don't send so often that people get annoyed.
List decay is natural. Email addresses get abandoned, people change jobs, domains lapse. A list that isn't maintained gradually fills with dead addresses that bounce. Running a re-engagement campaign every six to twelve months - and removing people who don't respond - keeps your list healthy.
Unengaged subscribers are people on your list who never open your emails. They're not bouncing or complaining - they're just silent. A large proportion of unengaged contacts drags down your overall engagement rates, which signals to inbox providers that your emails aren't wanted. Segment out unengaged contacts and either run a targeted re-engagement campaign or suppress them from regular sends.
#Sending behaviour and reputation
Beyond authentication and list hygiene, your sending patterns affect deliverability.
Warm up a new sending domain. If you've just set up a new sending domain or moved to a new email platform, don't immediately blast your entire list. Start with small volumes to engaged contacts, then gradually increase. ISPs need to see a history of good engagement before they trust a new sender.
Consistent sending cadence matters. Going quiet for two months and then sending five emails in a week looks suspicious. Consistent, predictable sending helps establish a pattern that ISPs recognise and trust.
Avoid spam trigger patterns. ALL CAPS in subject lines, excessive punctuation, image-only emails with no text, misleading subject lines - these all increase the likelihood of spam filter catches. Write emails that look like genuine communications from a real business, because that's what they are.
#How to diagnose a deliverability problem
If your open rates have dropped significantly and you haven't changed anything else, deliverability is the first thing to investigate.
Check your bounce rate and complaint rate in your email platform's reporting. If either has spiked, that's your starting point.
Use a tool like Mail-Tester or Google's Postmaster Tools to check your domain's reputation and authentication status. Postmaster Tools in particular will show you your spam rate as seen by Gmail - which is the inbox your subscribers are most likely using.
If you're on Klaviyo, the deliverability hub shows you your sending reputation and flags issues. Most major platforms have equivalent tooling.
If authentication records are missing or misconfigured, fix those first. Then address list hygiene. Then review your sending patterns. Reputation repair takes time - weeks to months depending on how badly it's been damaged - but it's recoverable.
#Frequently Asked Questions
What's the difference between "delivered" and "inbox placement"?
"Delivered" means the email reached the recipient's mail server. "Inbox placement" means it landed in their inbox rather than their spam folder or promotions tab. Most email platform dashboards show delivery rate, not inbox placement rate. The gap between the two is where deliverability problems hide.
How do I check if my domain is on a blacklist?
Use a free tool like MXToolbox to check your domain and sending IP against major blacklists. If you're listed, the tool will tell you which blacklist and typically how to request removal.
Does using a shared sending IP vs a dedicated IP affect deliverability?
Yes. On a shared IP, your reputation is partially tied to the behaviour of other senders using the same IP. A dedicated IP means your reputation is yours alone - but you have to warm it up yourself. For high-volume senders, a dedicated IP is worth considering. For most small businesses, a reputable platform's shared IP pool is fine.
How long does it take to recover from a bad sender reputation?
It depends on how bad the damage is. Minor reputation dips can recover in a few weeks with clean sending behaviour. Significant damage - being blacklisted or having sustained high complaint rates - can take two to three months of careful sending to repair. The earlier you catch it, the faster the fix.
Can using a free Gmail or Outlook address for business email hurt deliverability?
Yes. Sending marketing email from a gmail.com or outlook.com address looks unprofessional and many business contacts will mark it as spam. You should always send from an email address on your own domain (e.g. [email protected]).
#Don't let deliverability be an afterthought
Most businesses only think about deliverability when something has gone wrong. The smarter approach is to set it up properly from the start - authentication records in place, list hygiene practices established, sending patterns consistent - and check in on it regularly.
It's not exciting work. But it's the difference between an email program that reaches people and one that's quietly talking to itself in the spam folder.
This guide is written by Hedgehog, a DIY digital marketing consultancy specialising in small and medium businesses in Australia. We offer digital marketing consulting, coaching and training.
