Cold email deliverability checklist (2026): 14 things to fix before you hit send
Most cold email campaigns don't fail because the copy is bad. They fail because the emails never reach the inbox. This is the checklist we use ourselves — in order, with the actual numbers.
Domain and authentication
1. Never send cold email from your main domain
Buy 1–3 secondary domains (e.g. getacme.com, acme-team.com) and send from there. If a domain gets burned, your company email keeps working. Redirect the secondary domains to your real website so a curious lead lands somewhere legitimate.
2. Set up SPF, DKIM and DMARC on every sending domain
All three, no exceptions. Start DMARC at p=none with a reporting address, watch the reports for a couple of weeks, then move to p=quarantine. Google and Microsoft now reject or spam-folder bulk senders without authentication.
3. Use a custom tracking domain (or no tracking at all)
Shared tracking domains carry the reputation of everyone else using them. If you track opens or clicks, point a subdomain of your sending domain at your tool. Better for the first email: track nothing and send plain text.
Mailboxes and warm-up
4. Warm up every mailbox for 2–3 weeks before the first campaign
Warm-up means the mailbox exchanges real-looking emails with other real mailboxes, gets replies and gets pulled out of spam. Ramp gradually: 5 a day the first days, up to 30–40 a day by week three. Keep warm-up running at a low level even after you start sending.
5. Cap each mailbox at 30–50 cold emails a day
Volume is the most common mistake. Need 500 a day? Use 12–15 mailboxes across 3–4 domains, not one mailbox sending 500. Space sends 10–15 minutes apart and keep them inside business hours in the lead's time zone.
6. Use real business mailboxes
Google Workspace or Microsoft 365 accounts with a real name and a profile picture. Free Gmail or Outlook accounts get throttled fast.
List quality
7. Verify every email before you send
Syntax, MX record and a live mailbox check. Remove invalid addresses always; be careful with catch-all domains (you can't confirm the mailbox exists) — send to them in a separate, smaller campaign and watch the bounce rate.
8. Keep bounces under 2%
Above 3% mailbox providers start treating you as a spammer. Above 5% stop everything, find out why (bad list, catch-all domains, an old export) and fix it before continuing. A good tool pauses the campaign for you at that point.
9. Drop role addresses and duplicates
info@, sales@, contact@ almost never reply and often feed spam traps. Deduplicate by email and by company so you don't email three people at the same 10-person firm in the same week.
The email itself
10. Plain text, short, one idea
60–120 words. No images, no HTML templates, no link in the first email, no attachments. Write it like a note from one person to another. A first line that is actually about them (their company, their role, something they published) beats any template.
11. Avoid the words and formats that trigger filters
"Free", "guarantee", "offer", "discount", "urgent", ALL CAPS, exclamation marks, "$" signs and shortened URLs. Subject line: 2–5 words, lowercase or normal case, like an internal email ("quick question", "idea for {{company}}").
12. One low-friction call to action, and a way out
Ask for a reply or interest ("Want me to send the 2-minute video?"), not for a 30-minute call. Add a one-line, polite opt-out ("If this isn't relevant, just tell me and I won't write again"). It reduces spam complaints, which hurt far more than unsubscribes.
Sending and monitoring
13. Stop the sequence the moment someone replies
Follow-ups after a reply look like automation — because they are. Also stop on bounces and on out-of-office replies that indicate a wrong person. Space follow-ups 3–5 days apart; 2–3 emails total is plenty.
14. Watch four numbers every day
- Bounce rate — under 2%.
- Reply rate — 3–8% is healthy for a good list; if it drops suddenly, you are landing in spam.
- Spam complaints — near zero. Even 0.1% is a warning.
- Blacklists — check your domains and IPs weekly on MXToolbox.
Send a test to a few seed inboxes (Gmail, Outlook, a custom domain) before every new campaign and look where it lands.