Deliverability reports are full of numbers that look important and do not change what you should do on Monday. The useful set is small: acceptance, bounces, complaints, unknown users, and whether the people who got the mail actually did something. Inbox placement is a result, not a dashboard widget.
Acceptance vs inbox
Accepted by the MX is not the same as landing in the primary inbox. Seed tests and panel data estimate placement. Your SMTP logs only prove the receiving server took the message. Use both. If acceptance is high and seeds sit in spam, the problem is reputation or content, not routing.
The rates that get you blocked
Keep hard bounces and unknown users well under 2%, ideally far lower on a mature list. Stay comfortably under 0.1% spam complaints of delivered mail. A few tenths of a percent is an emergency. Treat spikes in Gmail Postmaster spam-folder behavior as product problems, not a template tweak.
These numbers are not vanity. They are how providers decide whether you still get to talk to their users.
Engagement is the long game
Mailbox providers watch whether recipients open, click, reply, move to inbox, or delete unread. A list that never engages will eventually be filtered even if authentication is perfect. Segment by recency. Stop mailing people who have ignored you for months.
Infrastructure signals
Track deferrals (4xx), blocklists, SPF/DKIM/DMARC pass rates, and TLS. A sudden 421 from Microsoft with a clean list often means you ramped volume or changed IPs too fast. Pair metrics with a timeline of what you changed: IP, domain, template, or audience.
A metric without a change log is trivia. A change log without metrics is folklore. You need both on the same page when something breaks.
A weekly ritual
Fifteen minutes: Postmaster spam rate, unknown-user rate, complaints, top 4xx by provider, and whether DMARC still passes. If any of those moved, look at campaigns shipped that week before you look at copy opinions.
Vanity metrics to ignore
Total sent, list size, and open rate without a complaint twin are how teams congratulate themselves while Gmail quietly files them away. If a metric cannot change whether you send tomorrow, it does not belong on the Monday dashboard.
