Check the number is real first
Opens are detected by a small tracking image loading. Some mail clients now pre-load images automatically for privacy, and others block them.
The result is that open rate is inflated for some recipients, absent for others, and varies by which mail client your audience happens to use.
Compare opens against clicks across your last few sends. If opens move and clicks do not, the opens are noise and there is nothing to diagnose.
If clicks are also low, it is a real problem
Then it is worth working out which one.
Signs it is a deliverability problem
This is the most common and least suspected cause. Emails are not being seen because they are not reaching the inbox.
A sudden collapse across all sends, not one campaign.
Low engagement from one mail provider specifically while others look normal.
Rising soft bounces, which often precede outright blocking.
Recent migration to a new platform without updating SPF and DKIM — the most common silent failure there is.
No authentication set up at all.
Test it: send to two or three different mail providers and see where it lands. If it is in spam, subject lines are irrelevant.
Signs it is a list problem
A large share of contacts have never engaged, including from the beginning.
The list was built quickly or from a source people do not remember.
Old contacts who have not opened anything in over a year.
High unsubscribes on recent sends, suggesting people do not want what you send.
Engagement is a rate, not a count — so a list where most people ignore you drags inbox placement down for everyone on it, including the people who do want to hear from you.
Signs it is genuinely the subject line
One send performed far worse than your usual, while others were normal.
Clicks fell in proportion, suggesting fewer people read it at all.
The subject overpromised and unsubscribes rose with it.
A single poor send is a subject line. A pattern across sends is not.
The order to fix things
- Authentication. SPF, DKIM, DMARC. Non-negotiable, and the fix for the most common cause.
- List hygiene. Remove hard bounces, prune long-dormant contacts.
- Frequency and relevance. Send when there is a reason.
- Subject lines. Last, and least.
Most businesses do this in reverse, spending weeks on subject lines while their mail lands in spam.
What a good subject line does
Specific, short, plainly informative. "Your AC before July" tells the reader what this is. "Don't miss our summer savings event!" sounds like a mailshot and gets sorted accordingly in under a second.
Where it sits
Deliverability setup and list management are part of email marketing setup at $650 a month.
Frequently asked questions
Is my open rate even reliable?
Less than it was. Some mail clients pre-load images and register opens nobody made; others block images and miss genuine reads. Compare opens against clicks — if opens move and clicks do not, it is noise.
How do I know if it is a deliverability problem?
A sudden collapse across all sends, low engagement from one provider specifically, rising soft bounces, or a recent platform migration without updating SPF and DKIM.
How do I know if it is a list problem?
A large share of contacts who have never engaged, a list built quickly or from a forgotten source, many contacts dormant over a year, or rising unsubscribes.
What order should I fix things in?
Authentication first, then list hygiene, then frequency and relevance, then subject lines last. Most businesses do this in reverse while their mail lands in spam.