Authentication, provider choice, warm-up and list hygiene that keep your emails in front of leads
Every email strategy rests on one assumption: that the email arrives. For many startups, that assumption is wrong. Messages land in spam folders or promotions tabs, and the team concludes that the copy or the offer failed when the real problem was delivery.
Deliverability is not luck. Mailbox providers such as Gmail, Outlook and Yahoo make placement decisions based on identifiable signals. This playbook explains those signals and gives you a system to manage them.
When an email arrives, the receiving system asks a series of questions. Is the sender authenticated? Does the sending domain and infrastructure have a good reputation? Have recipients engaged with this sender's mail before, or complained about it? Does the content look like something people want? The answers determine whether the email is accepted, filtered or placed in the inbox.
| Signal | What it means | What you control |
|---|---|---|
| Authentication | Proof the email really comes from your domain | SPF, DKIM and DMARC records |
| Reputation | Your domain and sending history | Volume growth, list quality, complaints |
| Engagement | Opens, replies, deletes, spam reports | Targeting and relevance |
| Content | Structure, links and formatting | Writing style and email design |
SPF lists the servers allowed to send email for your domain. Publish one SPF record and include every service that sends for you: your email provider, your CRM, your help desk.
DKIM signs each message cryptographically. The receiving server checks the signature against a public key published in your DNS. Your sending provider generates the key; you add the record.
DMARC tells receivers what to do when authentication fails and sends you reports. Begin with p=none to monitor, review the reports for a few weeks, then move to p=quarantine and eventually p=reject once all legitimate mail passes.
Key Insight: Authentication does not guarantee the inbox, but missing authentication almost guarantees problems. Set it up before you send your first campaign.
Since 2024, Gmail and Yahoo have required senders of large volumes to meet clear standards. Build to them even if your volume is small today:
Your sending provider manages the infrastructure your email travels through. Providers differ in tooling, infrastructure and how they manage sending reputation, and the same email can perform differently through different routes.
| Provider | Commonly chosen for | Consider when |
|---|---|---|
| Resend | Modern API, clean domain verification, product and transactional email | You want a simple, developer-friendly setup |
| SendGrid | Established platform for transactional and marketing email at scale | You need mature marketing and volume features |
| Mailgun | Detailed sending controls and logs | Your team wants granular technical control |
The best way to choose is to test. Send the same message to seed inboxes across major mailbox providers and your typical customers' business mail systems, and compare placement and engagement.
Send to your most engaged contacts only — customers and people who replied recently. Keep daily volume small.
Increase volume gradually. Watch bounces and complaints daily.
Add recent sign-ups and warm leads. Continue increasing only if engagement stays healthy.
Introduce broader segments in small batches.
Approach your normal volume. Pause increases if any metric worsens.
Operate at normal volume with weekly monitoring.
Use a closely related secondary domain for cold outreach so any reputation issues never affect invoices, password resets or customer communication from your main domain. Authenticate and warm it exactly like your primary domain.
| Metric | Healthy direction | If it worsens |
|---|---|---|
| Bounce rate | Low and stable | Clean the list; check capture sources |
| Complaint rate | Well below 0.1% | Review targeting, frequency and unsubscribe visibility |
| Reply and click rates | Stable or rising | Refresh content; tighten segmentation |
| Authentication pass rate | Near 100% | Check DMARC reports for unauthorised or misconfigured senders |
Salesqualifyd is a MarTech suite for startups and growing businesses. MPO Engine (Marketing Programs Optimisation) takes you from brand setup and buyer personas to a full-funnel GTM strategy, sprint-based execution, sales pitch, keyword plan, content with AI images, pitch deck and financial projections. CRM with follow-up reminders, email marketing through Resend, SendGrid or Mailgun, funnels and social complete the stack.
Learn more at salesqualifyd.com