Guide
The cold email infrastructure checklist
A checklist for teams running outbound from Instantly, Smartlead, Lemlist or similar, covering domains, DNS, mailboxes, warmup, volume, content and monitoring.
By Hamza Rivera, updated
Short answer: Cold email is bulk mail to the people who run the inboxes, so the same sender rules apply. Keep sending domains separate, authenticate every one, keep volume low and steady, verify your list, make opting out easy and watch the spam rate that Google and Yahoo publish thresholds for.
The short version
Cold email is bulk mail to the people who run the inboxes, so the same sender rules apply. Keep sending domains separate, authenticate every one, keep volume low and steady, verify your list, make opting out easy and watch the numbers that providers watch.
Domains
- Send from separate domains, not your main business domain, so a problem cannot reach your normal mail.
- Use domains you own and can explain to a recipient, with a working website and a clear business identity.
- Keep a list of every sending domain, what it is for and who owns the DNS.
- Forward the sending domains to your real site so recipients who look you up find you.
DNS records on every sending domain
- One SPF record per domain that lists the sending service and stays under 10 lookups.
- DKIM switched on, with the key published at the selector name in DNS.
- DMARC published, at least p=none with a report address. Gmail and Yahoo both name this as a minimum.
- A From domain that lines up with the SPF or DKIM domain.
- A custom tracking domain, if your platform offers one, set up with its own records.
Mailboxes
- A small number of mailboxes per domain, each a real looking sender with a signature and a name.
- Mailboxes created and given time to age before real sending starts.
- Everything documented: who owns each mailbox, which platform sends from it, which domain it belongs to.
Warmup and volume
- Warm up gradually and check the warmup is still running. Warmup tools differ, so follow the platform’s current guidance.
- Write down a daily and weekly cap per mailbox and keep real sending under it. New mailboxes get low caps that rise slowly.
- Spread a campaign over several mailboxes instead of loading one.
- Watch for sudden jumps. A quiet domain that suddenly sends a lot is exactly what providers flag.
Lists and content
- Verify addresses before sending. Bounces damage a domain faster than most people expect.
- Send to people with a plausible business reason to hear from you, and say who you are in the first lines.
- Include a clear way to opt out and honor opt-outs quickly. Yahoo asks for unsubscribes honored within 2 days.
- Keep emails short, plain and personal. Few links, no attachments, no shortened links.
- Respect the law where the recipient lives. This page is not legal advice.
Monitoring
- Verify each sending domain in Google Postmaster Tools. It shows spam rate for mail sent to personal Gmail, and gaps when volume is low.
- Keep the spam rate under the thresholds Google and Yahoo publish: under 0.10% as a target at Gmail, never reaching 0.30%, and under 0.3% at Yahoo.
- Read DMARC reports.
- Check blocklists on a schedule.
- Retire a mailbox or domain when its results fall, instead of pushing more mail through it.
Where to read next
If you run this for clients, see the white-label email deliverability page. For the rules behind the checklist, read the Gmail and Yahoo sender requirements and SPF, DKIM and DMARC in plain English.
Questions about cold email infrastructure
How many mailboxes per domain?
Few. There is no single number every provider agrees on, so keep it low, write it down and review it with your platform’s current guidance.
How many emails per mailbox per day?
It depends on the age of the mailbox and your platform’s guidance, which changes. The checklist advice is to set a written cap, start low, raise it slowly and cut it if bounces or complaints rise.
Do Gmail and Yahoo rules apply to cold email?
Yes. Mail is judged on how it is sent, not on what you call it. Authentication, valid DNS, low complaints and an easy way to opt out all apply. See the sender requirements guide.
Why did my open rates fall?
Common causes are an authentication change, a domain that grew too fast, bounces from an unverified list, a platform warmup that stopped and plain complaints. An infrastructure audit sorts the fixable ones from list and copy problems.
Does Passieon run cold email campaigns?
No. We audit and fix the infrastructure and can manage ongoing checks. We do not write or run your campaigns.
Is Passieon connected with Instantly, Smartlead or Lemlist?
No. Passieon is an independent agency. We work with whatever platform you use and have no connection with it.