- Deliverability, defined
- Deliverability is whether your mail reaches the inbox rather than the spam folder, which is a separate question from whether the receiving server accepted it at all.
Acceptance happens at the SMTP layer and is easy to measure: the server said 250 or it did not. Placement happens afterwards, inside the provider's filter, and no sender can see it directly.
The inputs are reputation, authentication, content and above all engagement. Gmail weighs whether people open, reply and move your mail out of spam far more heavily than anything in the message body.
Verification moves exactly one of those inputs. A high bounce rate is a loud negative signal, so removing dead addresses helps, and it does nothing at all about complaints or indifference.
Seed lists are how you observe placement. Send to accounts you control across the major providers and look at where the message landed, since that is the only visibility anyone outside the provider gets.
How ZapBounce reports it
We report on reachability, which is upstream of deliverability and not the same thing. A valid verdict means the mailbox accepted the recipient during our probe, and where your message lands after that depends on factors no verifier observes.
A 98.8% send that half the audience never saw
Imagine a campaign to 50,000 subscribers. The platform reports 49,400 accepted, which is 98.8%, and an overall click rate that's down a little. Nothing looks alarming until you split the results by mailbox provider.
Outlook and Yahoo recipients clicked at 2.1%, in line with past sends. Gmail recipients, who make up 27,000 of the list, clicked at 0.3%. Every one of those messages was accepted with a 250. A gap that wide at a single provider, with the others unchanged, almost always means the mail went to spam there.
Use clicks for this comparison, not opens. Apple's Mail Privacy Protection fetches images in the background whether or not a person reads the message, so open rates are inflated for anyone reading in Apple Mail, whichever provider hosts their mailbox. Clicks are lower and noisier, but a machine doesn't generate them on your behalf.
Working the problem in the right order
Start with what can be proven wrong. Send a test to a Gmail account, choose Show original, and confirm SPF, DKIM and DMARC all read PASS with your own domain. A failure here is the cheapest fix you'll ever make, and the rest won't matter until it's done.
Second, look at complaints. Google Postmaster Tools reports the spam rate Gmail recorded for your domain. If it sits above 0.3%, find the segment or source that's producing the complaints and stop mailing it.
Third, look at who you're sending to. If a large share of the list hasn't clicked anything in six months, you're teaching the filter that your mail gets ignored. Cutting those recipients feels like shrinking the program, and it's usually what brings the inbox back. Rewriting subject lines and removing so-called spam words belongs last, because content rarely overrides a poor sending record and a good record forgives a lot of clumsy copy.
Deliverability: common questions
What is a good deliverability rate?
Inbox placement above 90 percent across the major providers is healthy. Below 80 percent something in reputation, authentication or engagement is wrong.
Does verification improve deliverability?
It removes bounces, which is one input of several. If the problem is complaints or poor engagement, a clean list alone will not move placement.
How can I see whether mail reaches the inbox?
Seed accounts at each major provider, plus Google Postmaster Tools for Gmail. There is no report that shows placement across the whole audience.