This guide assumes inbox placement is already deployed and passing. It covers what breaks at scale and how mature teams operate it.
Edge cases that break a working setup#
- Trusting a single seed mailbox per provider; use several with different engagement histories.
- Optimizing for the seed test and not real recipient engagement.
- Mail forwarded through mailing lists or personal forwarders, which alters headers and content.
- Acquisitions and rebrands that introduce domains nobody audited.
- Vendors silently changing their sending infrastructure.
Operating it as infrastructure#
- Assign an owner for each sending domain and each vendor relationship.
- Put DNS records under version control or a change-review process.
- Alert on authentication pass rate drops and reputation changes, not just outages.
- Run a quarterly audit against the setup steps below.
- Document runbooks for the three most common failures.
Reference: the baseline setup#
- Create seed accounts at Gmail, Outlook, Yahoo, iCloud, and key B2B gateways.
- Send each campaign to the seed list before the full send.
- Record inbox, spam, promotions, and missing counts per provider.
- Correlate drops with content, sending domain, or list segment changes.
- Fix authentication, reputation, or content issues before scaling.
Frequently asked questions#
Why does mail land in Gmail Promotions?
Gmail classifies by content and sender behavior. Promotions is not spam and often performs well; do not over-optimize to escape it.
What is a good inbox placement rate?
Above 90% is healthy. Below 80% indicates a reputation or authentication problem.