Authenticate with SPF, DKIM and DMARC on every sending domain, keep spam complaints under 0.3% (aim for 0.1%), and make sure every domain can receive mail. The 5,000-a-day threshold is per domain and per provider, so cold emailers rarely hit it, but the rules are applied to everyone in practice.
The rules
Google and Yahoo published bulk sender requirements in 2024. Microsoft followed for Outlook in May 2025. By 2026 all three enforce them, and non-compliant mail gets permanent 550 rejections rather than the temporary errors of the first year.
| Requirement | Who | Cold email impact |
|---|---|---|
| SPF and DKIM on the sending domain | All senders | Every sending domain, not just the main one |
| DMARC, at least p=none, aligned with SPF or DKIM | Bulk senders | Set it on every domain anyway; it costs nothing |
| Spam complaint rate under 0.3% | Bulk senders | The number that kills cold email domains |
| One-click unsubscribe (RFC 8058) | Bulk marketing mail | Not required for one-to-one mail; a plain opt-out line is still wise |
| Valid forward and reverse DNS, TLS | All senders | Handled by Google Workspace or Microsoft 365 |
What “bulk sender” means
5,000 or more messages a day to that provider from one primary domain. A cold emailer sending 500 a day across five domains is not a bulk sender on paper. In practice, the filters apply the same logic to everyone; the threshold only changes how enforcement is described.
The two numbers
Complaint rate and bounce rate. Google says under 0.3% complaints, and that mitigation requests are only considered after seven straight days below it. The healthy target is 0.1%: one complaint per thousand delivered. Bounces should stay under 2%, which is a list quality problem, not a copy problem.
What to do this week
- Run every sending domain through the domain check.
- Verify each domain in Google Postmaster Tools and watch the spam rate graph.
- Verify your list before every send. Bounces compound.
- Add a one-line opt-out to cold sequences. It cuts complaints, which is the metric that matters.
Live SPF, DKIM, DMARC and MX lookup with raw records and plain-English fixes.
Questions
Does one-click unsubscribe apply to cold email?
Formally it applies to bulk marketing mail. For one-to-one cold email a plain reply-to-opt-out line is the common practice, and it reduces complaints, which is what protects you.
Is 5,000 a day counted across all my domains?
No. It is per primary sending domain, per provider. But filtering behaviour is the same below the threshold.
What complaint rate gets a domain blocked?
Sustained 0.3% or higher at Gmail causes throttling and spam placement. Aim for 0.1%.