Inbox placement is where an email ends up after it has been accepted: the primary inbox, a tab such as Promotions, or the spam folder. An email can be "delivered" and still never be seen.
Deliverability is not placement
Most sending tools report an email as delivered once the receiving server accepts it. That says nothing about the folder. For cold email, a message in spam is as good as a bounce, which is why placement is the number that matters.
How to measure it
- Placement tests: send one real email to test inboxes at the main providers and see which folder each lands in. mailzy runs these from your own mailboxes and shows the result per provider.
- Warm-up figures: warm-up emails are sent to real mailboxes, so their inbox and spam rates show how a mailbox is doing day to day.
- Reply rates: a campaign that suddenly gets no replies is often landing in spam.
What improves it
Authentication, a warmed-up mailbox with a good reputation, modest daily volume, a verified list and short, plain emails without heavy links or images.