Cold Email Deliverability Checklist: Domains, DNS and Warm-up

Key takeaways

• Never send cold email from your main company domain. Use secondary domains and protect your primary one.
• Gmail and Yahoo require authentication, easy unsubscribe and low spam complaint rates from bulk senders.
• Warm up new mailboxes slowly, cap daily volume and verify every list before you send.

AI makes it easy to write and send more email. It also makes it easy to burn your domain. When reputation drops, everything suffers: cold outreach, replies to customers and even invoices land in spam.

This is the checklist we use when we set up outbound infrastructure for clients. Work through it before your next campaign.

1. Domains

2. Authentication (SPF, DKIM, DMARC)

Mailbox providers now expect proper authentication. Since February 2024, Google requires bulk senders to:

• authenticate mail with SPF and DKIM;
• publish a DMARC policy;
• support one-click unsubscribe for marketing and promotional mail;
• keep spam complaint rates below 0.3%.

Yahoo introduced similar rules at the same time. Even if you don’t hit bulk volumes, meeting the same standard is the safest way to stay in the inbox.

3. Mailboxes and warm-up

• Create a small number of mailboxes per domain, each with a real name, photo and signature.
• Warm up every new mailbox gradually. Start with a small number of emails a day and increase over several weeks.
• Keep a steady, human-looking pattern. Sudden spikes are a red flag.
• Spread volume across mailboxes and domains instead of pushing one mailbox hard.

4. Lists

Bad data is the fastest way to a bad reputation. Before every campaign:

• Verify every address and remove invalid, risky and catch-all addresses you can’t confirm.
• Target narrowly. Relevance keeps complaint rates down. Our guide on signal-based outreach explains why fewer, better-timed emails win.
• Honour opt-outs immediately, across every domain and tool.

Vendor research shows how this goes wrong at scale: Laxis reports that domain-reputation problems from over-sending stop a large share of AI SDR rollouts within the first 90 days.

5. Content

• Write like a person: short, plain text, one clear ask.
• Avoid heavy images, attachments and lots of links in first-touch emails.
• Personalise with a real reason to reach out, not a mail-merged compliment.
• Keep human review on AI-drafted outreach until you’ve proven quality. Our email agents work with rep approval for exactly this reason.

6. Monitoring

If any metric slips, pause that mailbox or domain, find the cause and ramp back up slowly.

Where AI fits, and where it doesn’t

AI is useful for the research and drafting that make each email relevant: reading the account, finding a real trigger and writing a first line that references it. That relevance is what keeps complaint rates low.

Where AI hurts is volume. The easiest way to burn a domain is to let an agent send thousands of near-identical emails because it can. Keep sending limits in your infrastructure, not in the agent’s good judgement, and keep a person reviewing first-touch emails until the data shows quality is consistent.

The best setups use AI to send fewer, better emails, not more of them.

Don’t forget the phone

The same thinking applies to calling. Register caller IDs and monitor number reputation, so your calls aren’t labelled as spam. We set up email and calling infrastructure together.

The bottom line

Deliverability isn’t a one-time setup. It’s infrastructure plus discipline: separate domains, proper authentication, slow ramps, clean lists, relevant messages and weekly monitoring. Get it right and every campaign starts from a healthy baseline.

Sources

• Google, Email sender guidelines
• Yahoo, Sender best practices
• Laxis, State of AI SDR 2026