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.
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
- Hard bounces / unknown users: keep well under 2%, ideally far lower on a mature list.
- Spam complaints: stay comfortably under 0.1% of delivered mail. A few tenths of a percent is an emergency.
- Unsubscribe and spam-folder clicks on Gmail Postmaster: treat spikes as product problems, not a template tweak.
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.
