Most business owners assume a bad open rate means the subject line was weak or the timing was off. In practice, when I get called in to look at why a client’s emails aren’t performing, the writing is rarely the problem. The email never reached the inbox to be opened in the first place. It landed in spam, got filtered into Promotions, or was silently dropped by the receiving server before a human ever saw it existed.
Deliverability is invisible until you know exactly where to look, which is exactly why it gets misdiagnosed as a content problem for months. Here’s what’s actually going on, and what fixes it.
Start by Finding Out Who’s Actually Sending Your Email
Before chasing DNS records, there’s a diagnostic step that gets skipped constantly, even by people who’ve been sending email marketing for years: find out how your email is actually being delivered. Not what it looks like - your logo, your colours, your template - but the technical domain it’s genuinely sent from. You can only see this by checking the real “From” address rather than the display name, or opening a test email’s full headers (Show Original in Gmail, View Source in Outlook) and looking at the Return-Path.
If the email is sent on behalf of your own domain - the address is genuinely something@yourbusiness.com.au - the DNS-side setup absolutely matters, and that’s what the rest of this section covers.
If the platform sends from its own domain and only the visual branding is yours - the address is something like yourbusiness@somemarketingtool.net, just styled to look like you - your own domain’s DNS is irrelevant to this check. The platform is fully responsible for its own domain’s authentication, and it already handles that for every customer sending through it. Chasing SPF records on your own DNS in that setup is a wasted afternoon; the diagnosis needs to move straight to complaint rate and reputation instead, covered below. Worth knowing the trade-off either way: sending on your own domain builds reputation you own long-term, but you carry the full setup burden. Sending from a shared platform domain means authentication is handled for you, but you’re also sharing sending reputation with every other business using that same domain.
If It’s Your Domain: Authentication Is the Root Cause, Not Your Copy
The single most common issue I find when auditing a struggling setup that does send on the business’s own domain isn’t the subject line - it’s that SPF, DKIM, and DMARC were never configured properly, or configured at all. These are DNS records that prove to a receiving mail server that an email genuinely came from your domain and hasn’t been tampered with. Without them, you’re asking Gmail and Outlook to trust a stranger.
If you’re sending through an ESP like Mailchimp or MailerLite on your own domain, this isn’t something you configure from scratch - it’s their “domain authentication” or “sending domain verification” step, which adds specific CNAME records they provide to your DNS. It sits one click away from “just start sending a campaign,” so it’s one of the most commonly skipped steps I see - not because the platform hides it, but because nothing forces you to complete it before your first send goes out. Check for a “Verified” status against your sending domain in the platform’s settings; anything less means this is very likely your answer.
This isn’t a minor technical footnote anymore. Since November 2025, Gmail permanently hard-rejects non-compliant bulk mail before it reaches spam - the email doesn’t land anywhere, it just vanishes. Microsoft has enforced the equivalent since May 2025. If you’ve ever sent a campaign and watched the numbers come back suspiciously low with almost no bounces recorded, this is very often why: the email wasn’t bounced, it was rejected outright and never counted.
To be fair about scope: the strict enforcement threshold Google applies is 5,000+ emails per day to personal Gmail accounts, and most small business lists never get near that volume. But the underlying signal doesn’t stop mattering below that line - inbox providers use SPF, DKIM, and DMARC as a baseline trust check for senders of any size in 2026, not just bulk senders. I’ve seen plenty of 300-subscriber lists sitting in spam for the exact same reason a 50,000-subscriber list would. Skipping authentication is the most common, and most completely fixable, cause of poor deliverability I see - for businesses sending on their own domain.
The Metric That Actually Decides Your Fate
If authentication is set up correctly and deliverability is still poor, the next thing I check is spam complaint rate - and it’s usually the answer. Google Postmaster Tools surfaces this number prominently because inbox providers weight it more heavily than almost anything else when deciding where your next email lands. Roughly 0.1% is considered the safe ceiling - past that, your sending reputation starts degrading, and it degrades for every email you send afterwards, not just the ones that triggered it.
Complaint rate climbs for one predictable reason: sending to people who don’t actually want to hear from you. Purchased lists are the worst offender, but cold or long-unengaged contacts on an organically built list do the same damage slowly. If you built your list properly in the first place, this is a smaller problem - but even a clean list needs periodic pruning of people who’ve stopped opening.
Reputation Is Earned Gradually - You Can’t Skip the Queue
Here’s a mistake I see constantly with new senders: a business sets up a fresh domain, builds a list for a month, then sends the full list in one blast on day one. To an inbox provider, that pattern - a brand-new sender suddenly pushing high volume with no sending history - looks identical to spam behaviour, because it’s exactly what spam behaviour looks like.
The fix is warming up: start by sending to your most engaged 10-20% of contacts, let a few days of good open rates build a track record, then gradually widen the send. It feels unnecessarily slow the first time you do it. It’s also the difference between a domain that lands in the inbox reliably within a month and one that fights spam filters for its entire life.
The Content Mistakes That Still Trip People Up
Once authentication and reputation are sorted, content still matters at the margins:
- Spam-trigger subject lines - excessive punctuation, ALL CAPS, and words like “FREE” or “ACT NOW” still get flagged by filters, even in 2026
- A poor text-to-image ratio - an email that’s a single large image with almost no text reads as suspicious to filters, not just to humans
- A broken or missing one-click unsubscribe - this isn’t optional under the Spam Act, and it also directly affects deliverability, because an unsubscribe that’s hard to find is what turns an uninterested reader into a spam complaint instead
The Practical Checklist
If your open rates have been quietly bad and you’re not sure where to start:
- Check your real “From” address or email headers first - confirm whether you’re sending on your own domain or a platform’s shared domain, since that determines whether the next step even applies to you
- If it’s your domain, check your SPF, DKIM, and DMARC records - a free tool like MXToolbox will tell you in under a minute whether they’re configured and passing, or check for a “Verified” domain status in your ESP’s settings
- Set up Google Postmaster Tools - it’s free, and it’s the only place you’ll see your actual spam complaint rate and domain reputation, rather than guessing
- Prune unengaged subscribers - anyone who hasn’t opened in 90-plus days is doing more harm to your reputation than good sitting on the list
- Warm up new sending domains - start small, build a track record, then scale volume
- Review your last few subject lines and templates - fix the obvious content flags, but only after the technical foundation is actually solid
Deliverability problems get blamed on writing far more often than they’re caused by it. Fix the infrastructure first - the copy was probably fine all along.
Frequently Asked Questions
What’s the difference between SPF, DKIM, and DMARC?
SPF lists which mail servers are allowed to send email on behalf of your domain. DKIM adds a digital signature to each email proving it wasn’t altered in transit. DMARC tells receiving mail servers what to do if an email fails either check - reject it, quarantine it, or let it through - and gives you visibility into who’s sending mail as your domain. All three work together; having only one or two configured leaves gaps a receiving server can flag.
How do I check if my SPF, DKIM, and DMARC records are set up correctly?
A free tool like MXToolbox will check all three in under a minute and tell you exactly what’s missing or misconfigured. If you’re sending through an ESP like Mailchimp or MailerLite, check for a “Verified” domain status in the platform’s settings instead - that confirms the same thing without needing to read raw DNS records.
Does a high open rate mean my deliverability is good?
Not necessarily. Open rate only counts emails that reached an inbox and were opened - it says nothing about the emails that were silently rejected or dropped before delivery, which don’t show up as a bounce or appear in your stats at all. A healthy open rate on a shrinking list, or one that’s dropped suddenly with no clear cause, is often a sign that a portion of your sends are vanishing before they’re ever counted.
If your email open rates don’t add up and you want someone to actually diagnose your email marketing setup, get in touch to find out how YourStuff can help.
Photo by CHUTTERSNAP on Unsplash
