When people say they are getting blocked, they usually mean one of three things: hard bounces, spam-folder placement, or provider-side throttling on a mailbox or domain. Copy tweaks rarely fix those. The fix order is boring on purpose: prove identity, earn reputation, respect limits, keep lists clean.
For the full 2025 checklist in one place, read Cold Email Deliverability Best Practices 2025. This post focuses on the “blocked” symptom and what to change first.
Scaling without torching domains is a strategy problem too—see protect domain reputation while scaling outbound.
1. Authentication before volume
If SPF, DKIM, and DMARC are wrong or drifting, you are not having a “deliverability debate”—you are failing the front door test. Audit after every DNS or provider change.
SuperSend surfaces domain and sender health inside deliverability infrastructure for common setups (Google Workspace, Microsoft 365, Mission Inbox, and others).
2. Warm up new mailboxes like a real operator
A fresh mailbox that jumps to full list size reads like automation to filters. SuperSend runs built-in two-phase email warmup: an initial ramp (tracked as days of ramp) and background warming afterward.
Critical detail: Warmup and campaign sends share the same per-sender daily ceiling. If campaigns consume the whole budget, warmup cannot do its job—and vice versa.
3. List quality is a blocking lever
Hard bounces and garbage addresses are not minor stats. They are signals that spread across your domain pool.
- Validate before you scale
- Remove hard bounces immediately
- Stop hammering chronic soft bounces
On SuperSend, email validation uses global credits (one credit per validation on Growth and Scale plans). Placement tests use credits too (five credits per seed). Credits are included with the plan, but they are not unlimited—budget them like ad spend.
4. Velocity, rotation, and provider caps
One inbox cannot carry enterprise throughput without pain. Spread load across multiple warmed mailboxes and sending domains with disciplined rotation.
Google, Microsoft, and SMTP hosts enforce the hard stops—not your sequencer. If you need more sends, you need more healthy identities, not louder subject lines.
5. Content and complaints (the part copy actually affects)
Heavy HTML, link walls, and “marketing voice” increase scrutiny early in a relationship. So does irrelevant targeting.
Complaints hurt more than a polite opt-out. Make it easy for someone to stop hearing from you, honor requests promptly, and keep your from identity honest. Rules vary by region and use case—treat compliance as a requirement, not a blog footnote.
6. Do not confuse cold outbound with newsletter tools
Mailchimp-class tools are built for permissioned marketing mail. Cold outbound is a different job: you still need authentication, warmup, and reputation discipline—but the product category and risk profile are not interchangeable.
SuperSend is a cold email and LinkedIn sequencer that connects to your sending infrastructure (buy domains and mailboxes in-app, or connect providers via API/OAuth, SMTP, and the integrations we support). It is not a transactional ESP replacement for product email—and we do not pretend it is.
If you only fix three things this week
- DNS authentication is correct and aligned
- New mailboxes are warming on a real schedule, with campaign volume budgeted against the same daily ceiling
- Lists are validated and bounces are handled aggressively
Then—and only then—worry about clever templates.
Related Articles
Deep dives
- Cold Email Deliverability Best Practices 2025
- Cold Email Infrastructure: The Complete Guide to Scaling Safely
