Advanced bulk sender requirements: edge cases, scale, and monitoring

This guide assumes bulk sender requirements is already deployed and passing. It covers what breaks at scale and how mature teams operate it.

Edge cases that break a working setup#

• Thinking the rules only apply above 5,000; Gmail applies most of them to all senders.
• Using a gmail.com From address for bulk mail, which fails DMARC alignment.
• 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#

1. Assign an owner for each sending domain and each vendor relationship.
2. Put DNS records under version control or a change-review process.
3. Alert on authentication pass rate drops and reputation changes, not just outages.
4. Run a quarterly audit against the setup steps below.
5. Document runbooks for the three most common failures.

Reference: the baseline setup#

1. Publish SPF and DKIM, and a DMARC record at minimum p=none with aligned From domain.
2. Add List-Unsubscribe headers and honor requests within two days.
3. Use a valid forward and reverse DNS (PTR) for sending IPs.
4. Monitor spam rate in Postmaster Tools and keep it under 0.1%.
5. Send from a subdomain with its own reputation for marketing.

Frequently asked questions#