The 27 Rules of Cold Email We Enforce on Every Campaign (2026)

There are 27 rules we enforce on every cold email campaign we run: 9 copy rules, 4 sequence rules, 5 infrastructure rules, 4 list rules and 5 measurement rules. They are not suggestions or best-practice garnish. Each one exists because breaking it cost a real campaign real money, and each one is enforced as a hard gate before and during every send.

We run cold email for clients at up to 50,000 sends a month per client, and everything below comes straight out of the internal doctrine our team and our automation actually execute. If you only take one thing: most cold email fails on the boring rules, not the clever ones.

What are the cold email copy rules?

Copy rules exist to make an email read like one busy human writing to another, and to keep spam filters out of the conversation. Nine rules cover it.

1. Keep every email to 6 lines and 120 words maximum. Shorter wins, and our variant sets run from about 30 words to about 100. If a word is not doing work, it goes.
2. Use the prospect's first name inline, and drop the "Hey". Opening the sentence with their name reads like a colleague getting to the point; a greeting line is a wasted line in a 6-line format.
3. Make the CTA a value question, never a favour. "If I put this together for you, would that be useful?" puts the decision on them to evaluate value. "Happy to help" and "we'd love to show you" give away power, and "worth a chat?" is banned outright.
4. Never mention calls, meetings or time in a cold email. Asking a stranger for 30 minutes is the biggest ask in the message and it kills replies. The CTA is a pure interest check; the call comes later, after they have raised their hand.
5. Put zero links, URLs, email addresses or dotted domains in the copy. Anything that renders as a link from an unknown sender is a spam signal. When a company name must appear, write it with a dash instead of a dot. The full reasoning is in our post on links in cold email.
6. Send plain text, one sentence per line. HTML templates scream marketing, and walls of text scream effort. A line break after every sentence is how real people write short emails.
7. Keep subject lines to 2 to 4 lowercase words that a colleague could have sent. The company name alone, "quick question" or a plain industry reference consistently beat creative subject lines. Anything that reads like a newsletter gets rewritten.
8. Scan every subject and body for spam words, and substitute rather than ship. The number one offender is "free": we always write "on us" or "no charge" instead. The scan re-runs after every edit, including edits the client asked for, because a client request does not override a spam filter.
9. Write the ps line lowercase, and spend it on proof. The ps is often the most-read line in the email, so it carries a specific, numbered proof point rather than a repeated ask.

What are the cold email sequence rules?

Sequence rules protect deliverability and stop follow-ups from becoming nagging. Four rules cover it, and the structural template is fixed.

10. Leave a minimum of 3 days between any two steps. Tighter gaps read as pestering and inflate per-domain volume. Deviations from 3 days happen, but they must be deliberate, never accidental.
11. Run the standard 4-step architecture. Step 1 opens; step 2 follows up 3 days later in the same thread; step 3 lands 30 days on; step 4 follows 3 days after that in step 3's thread. Four touches is the default, not a starting bid for twelve.
12. Make step 3 a different offer in a new thread. A month after the first touch the prospect has forgotten you, which makes step 3 a second first-impression. Re-sending the same pitch in the same thread wastes it; a fresh subject and a fresh offer effectively doubles the campaign.
13. Every follow-up must add new material. A new angle, a new insight or a specific case-study result with a number, never "just bumping this". A follow-up that adds nothing teaches the prospect that your emails can be safely ignored.

What are the cold email infrastructure rules?

Infrastructure rules are the ones nobody sees when they work and everybody feels when they fail. Five rules cover it.

14. Warm up every sender account for 2 to 3 weeks before real volume. A cold domain sending cold email at volume from day one is how sending reputations die before the first reply arrives.
15. Start every sender at 1 email per day, and scale to around 3 only after the offer is proven. The proof is interested replies arriving consistently on one offer, with quiet bounces as the safety gate. Volume is earned by signal, not by the calendar.
16. Send from secondary domains only, never the main company domain. Cold sending carries reputational risk, and that risk must never touch the domain the business runs on. Secondary domains redirect to the main website.
17. Run 3 sender accounts per domain, no more. It spreads volume enough to matter while keeping each domain's footprint natural. Overloading one domain concentrates exactly the risk this structure exists to spread.
18. Turn open tracking off. Tracking pixels are a spam signal from senders with no reputation, and open data is noise anyway. Measure on replies, which are real.

What are the cold email list rules?

The list is where campaigns are won or quietly lost before a single word is written. Four rules cover it, and every one is a launch gate in our pre-launch checklist.

19. Freshly verify every email address before upload. Stale "valid" flags from old exports count for nothing: we watched a list where 582 leads carried a valid flag, around 140 passed fresh verification, and the campaign hit a 45% bounce rate before anyone caught it.
20. MX-check every unique domain in the send set, never a sample. A 40-domain spot-check on one of our lists came back clean while the full sweep of all 6,872 domains found the problem leads. A full sweep costs minutes; a missed gateway costs a sending domain.
21. Strip every lead behind a strict security gateway, such as Mimecast or Barracuda, before sending. These gateways reject new-sender cold mail on policy, regardless of address validity. On one campaign, Mimecast recipients were 7% of the list and 77% of all bounces. Remove them silently, every time.
22. Temperature-check the list before blaming the copy. Sample the addresses you actually sent to and read the non-interested replies. If the people are wrong, no rewrite fixes it; a great offer still fails on the wrong list.

How do you measure a cold email campaign?

Measurement rules stop you optimising the wrong number or calling winners on noise. Five rules cover it, anchored to the benchmarks below.

23. Judge campaigns on interested replies per send, not on reply rate. Reply rate is a deliverability signal: it tells you the emails are landing. Interested rate is the offer signal: it tells you the message is working. A healthy reply rate with zero interested replies means the offer is the problem.
24. Make no variant decisions before roughly 1,000 sends per variant. Below that floor the differences are noise, and the first low-volume week is infrastructure validation, not a copy test.
25. Kill or rebuild an offer at roughly 2,000 cumulative sends and 20 replies with interest still low. At that point "too early" is no longer true. The offer has been tested and it does not land; testing more copy on top of it burns list.
26. Test one variable at a time against a control. Change the subject line, the opener, the ps or the CTA, never several at once. After about 5 such tests, composite the winners into a new champion and make it the control, as covered in our reply rate benchmarks.
27. Reallocate volume the same day a density winner appears. Rank variants on interested replies per send. "Every variant got at least one interested reply" is not a tie; the variant earning interest at twice the density gets the volume today, not after another polite week of even splits.

The benchmark tiers we measure against

Metric	Underperforming	Okay	Good	Really good
Reply rate (deliverability signal)	Below 0.5%	0.5 to 1%	1 to 1.5%	Above 1.5%
Interested share of replies (offer signal)	Below 5%	5 to 10%	10 to 20%	Above 20%
Sends per interested reply	Above 1,000	Approaching 1,000	500 to 1,000	Below 500

One warning on reading the table: judge reply rate against the list's mailbox mix. A list full of enterprise domains behind strict gateways will run lower than a startup-heavy list at identical quality, so a low rate against the wrong baseline is not a broken campaign. A good offer still has to earn interested replies at any baseline.

What happens when you break the rules?

You find out slowly, which is the dangerous part. A spam word does not bounce your campaign on day one; it erodes inbox placement over weeks. An unverified list does not fail loudly; it burns your sending domains while the dashboard still shows sends going out. That delay between the mistake and the consequence is exactly why these are enforced as gates rather than remembered as tips.

It is also why every rule here is enforced by checklist and automation rather than by memory. We learned that the hard way: a single client-requested word swap once went to a live campaign without a re-scan, reintroduced our number one banned spam word, and cost us deliverability we then had to rebuild. Humans skip steps on the tenth repetition. Gates do not.

If you want the rules in build order rather than rulebook order, start with how to write a cold email for the copy layer, then run the pre-launch checklist before anything goes live. The rules are free. The discipline to enforce all 27 on every campaign is the actual product.

FAQ

How many cold emails should you send per day per sender?

One email per sender per day while the offer is unproven, rising to around 3 per day once meetings are booking consistently off one offer. Sender accounts need 2 to 3 weeks of warmup first, and 3 sender accounts per domain is the standard structure.

How many words should a cold email have?

Six lines and 120 words maximum, and shorter usually wins. Our variant sets run from roughly 30 words at the short end to about 100 at the long end. Every sentence gets its own line, and every word that is not working gets cut.

What is the best time to send cold emails?

Business hours in the recipient's own timezone, and skip public holidays, when reply rates tank. Beyond that, send timing matters far less than the list, the offer and deliverability. Nobody replies to the wrong offer because it arrived at the perfect hour.

How many follow-ups should a cold email sequence have?

Our standard cold sequence is 4 steps: the opener, a follow-up 3 days later in the same thread, a new offer in a new thread 30 days on, and a final follow-up 3 days after that. Never less than 3 days between any two steps.

Can you include a link in a cold email?

No. No URLs, no email addresses, no dotted domains anywhere in cold copy, because link patterns from an unknown sender are a spam signal. Write the company name with a dash instead of a dot and make the call to action a reply, not a click.

What is a good cold email reply rate?

Total reply rate of 0.5 to 1% confirms you are landing in the inbox, and above 1.5% is really good deliverability. The metric that decides money is interested replies: 10%+ of replies interested is good, 20%+ is great, and under 500 sends per interested reply is really good.