What is email delivery rate?
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Email delivery rate is one of those metrics that sounds more reassuring than it actually is. A 99% delivery rate doesn't mean 99% of your emails landed in the inbox. It means 99% of your sends weren't rejected at the server door.
The formula: emails accepted by the receiving server / total emails sent x 100.
Every email either gets accepted (delivered) or rejected (a bounce). Delivery rate only counts the acceptance. What happens after that (inbox, spam folder, promotions tab, deleted before it's read) isn't part of the calculation.
What delivery rate doesn't tell you
A 99% delivery rate with 40% spam placement means most of your "delivered" mail is going straight to junk. Delivery rate doesn't capture that. Inbox placement rate does, but measuring it requires seed list monitoring tools that most ESPs don't provide out of the box.
This distinction matters because a lot of senders assume delivery rate and deliverability are the same thing. They're not. Delivery rate is a floor, not a score.
When delivery rate signals a real problem
Under 95% usually means your list has significant hygiene issues. Hard bounces (invalid addresses, dead domains) and repeated soft bounces (full mailbox, temporary failures) both pull the rate down. Under 90% is serious. Most ESPs will throttle your account or flag it for review at that point.
If your delivery rate is dropping, the first thing to check is whether you're accumulating hard bounces from stale or invalid addresses. Our list cleaning strips those before they become a problem. If something broke suddenly, the SOS hotline is free.
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