A cold email that lands in spam was never sent, as far as the reader is concerned. Deliverability is not one setting; it is the reputation your domains and inboxes build with mailbox providers over time. This guide explains what deliverability is, how to set up sending domains and the three records that prove your mail is yours, what warm-up does, how to keep lists and volume clean, what in an email trips filters, how to monitor it, and how to recover a domain that has gone bad.
01
What cold email deliverability is
When you send an email, the receiving mailbox provider decides one of three things: deliver it to the inbox, deliver it to spam, or reject it. It decides mostly on reputation: the history of your sending domain and inbox, whether your records prove the mail is really from you, how people react to your messages, and what the message itself looks like.
Reputation is built slowly and lost quickly. That is why every step below is about protecting it, and why it belongs at the start of any outbound system, not after the first campaign goes wrong.
02
Set up separate sending domains
Do not send cold email from the domain your company uses for everything else. If its reputation suffers, your invoices, support replies and hiring emails suffer with it. Buy one or more domains close to your brand, point their web address at your main site, and send cold email only from those.
- Pick names a reader will recognise. A small variation on your brand, not a random string.
- Use a mainstream email provider for the inboxes. Real mailboxes on a known provider look like real people.
- Give each inbox a real name and signature. One person, one inbox.
- Let new domains age. A domain registered yesterday has no history, and providers treat it with caution.
03
SPF, DKIM and DMARC, in plain words
These are three records you add to each sending domain's settings. Together they let a mailbox provider check that an email claiming to come from your domain really did.
Who may send
SPF
A list of the servers allowed to send email for your domain. Mail from anywhere else looks suspicious.
Proof it is unchanged
DKIM
A digital signature added to each email, checked against a public key on your domain. It shows the message was not altered on the way.
What to do if checks fail
DMARC
A policy that tells providers what to do with mail that fails the first two checks, and where to send reports about it.
Your email provider gives you the exact values to paste in. After adding them, send a test email to yourself and check that all three pass; most mail apps show this in the message details. Large mailbox providers have tightened their rules, and unauthenticated mail is increasingly filtered or rejected.
04
Warm-up, and what warm-up tools do
Warm-up builds a new inbox's reputation before it sends cold email. You start with a few emails a day and raise the number gradually over a few weeks.
Warm-up tools automate this. They connect your inbox to a network of other inboxes that send each other ordinary-looking messages, open them, reply, and move them out of spam if they land there. To the provider, your inbox looks like one people write to and read.
- Start low and raise it weekly. Jumping straight to a high daily number defeats the point.
- Keep warm-up running at a low level after cold sending starts, so good signals keep coming.
- Check what was actually sent, not just that warm-up is switched on.
How long to warm up, and how fast to raise volume, is covered in how many cold emails per day per domain.
05
Sending limits
Volume is where most domains get burned. Keep each inbox to a modest number of cold emails a day, spread them through the working day rather than in a burst, and grow by adding inboxes and domains rather than pushing one inbox harder. If replies fall or bounces rise, slow down before you do anything else.
06
List hygiene and bounces
Every email to an address that does not exist is a bounce, and a high bounce rate tells providers you are not sending to people who know you.
Verify every address before sending. Run the list through an email verifier and remove invalid addresses.
Be careful with catch-all domains. Some domains accept every address, so a verifier cannot tell if a person exists. Send to them in small amounts, or not at all.
Stop on a hard bounce. An address that bounced once as "does not exist" should never be emailed again.
Skip shared addresses. Addresses like info@ or sales@ are read by several people and complained about more often.
Do not reuse old lists. People change jobs; a list from last year has quietly gone bad.
07
Content that trips spam filters
- Links and images. Keep the first email to plain text, with no images and at most one link, ideally none.
- Tracking. Open and click tracking adds hidden images and rewritten links. Many senders turn it off for cold email.
- Attachments. Never in a first cold email.
- The same text to everyone. Identical messages sent at volume look like bulk mail. A real, specific first line per person helps.
- Marketing language. Capitals, exclamation marks and pushy phrasing read as an advertisement, to filters and to people.
Short, plain and specific is better for deliverability and for replies. See how long a cold email should be and our cold email templates.
08
Monitoring your deliverability
Placement tests. Send to a set of test inboxes across providers and see how many land in the inbox, spam or promotions. Do it before a campaign and every few weeks after.
Bounce rate. Watch it per campaign and per inbox. A rise usually means a bad list.
Replies, by what they say. A sudden drop in replies can be the first sign mail has moved to spam.
Complaints and unsubscribes. People marking you as spam is the strongest negative signal there is. Make it easy to say no instead.
The providers' own dashboards. Large mailbox providers offer free sender dashboards showing your domain's reputation and spam rate.
09
Recovering a burned domain
- Stop cold sending from it at once. Every extra email makes the reputation worse.
- Find the cause. A bad list, a sudden jump in volume, a broken record, or content that changed.
- Check public blocklists for the domain, and request removal once the cause is fixed.
- Warm it up again slowly, as if it were new, and test placement before sending again.
- Know when to retire it. Sometimes a fresh domain is faster than repairing an old one. This is why cold email never goes out from your main domain.
10
Common deliverability mistakes
Sending from the main company domain. One bad week can affect every email the company sends.
Skipping warm-up to launch faster. It saves a few weeks and can cost the domain.
Trusting a setting. "Warm-up on" or "records added" means nothing until you check the result.
Buying a list and sending to it unverified. The bounces alone can damage a new domain.
Scaling one inbox instead of adding inboxes. Volume per inbox is the easiest number to get wrong.
11
The deliverability checklist
Before the first cold email goes out
- Cold email goes out only from separate sending domains.
- SPF, DKIM and DMARC pass on a test email from every inbox.
- Every inbox has warmed up for several weeks, and you checked what it actually sent.
- Daily volume per inbox is modest, spread through the day.
- Every address was verified, and catch-all domains are handled with care.
- The first email is plain text, with no attachments and no tracking you do not need.
- A placement test went to the inbox, not spam.
What we have seen"Warm-up on" is a setting, not proof. New inboxes on new domains showed warm-up as active and had sent nothing; the one that worked had sent 205 warm-up emails in 7 days. We never confirmed the cause, so now we read what each inbox actually sent before trusting it.
12
Questions
How long does it take to warm up a cold email domain?
Plan on several weeks before full cold sending, starting low and raising volume weekly. The sibling guide on daily volume per domain covers the timing in detail.
Do I need DMARC for cold email?
Yes. Large mailbox providers increasingly expect SPF, DKIM and DMARC together, and mail without them is more likely to be filtered.
Should I track opens in cold email?
Many senders turn open tracking off for cold email, because it adds hidden images and its numbers are unreliable. Replies are the measure that matters.
Should I use my real name for cold email?
Yes. Send from a real person who will answer the replies, under their own name, with a matching signature. A made-up sender falls apart as soon as someone replies, looks you up or asks for a call. In the US, the CAN-SPAM Act requires the From line to be accurate and to identify who sent the message, and it makes no exception for business-to-business email.
13
Where to go next
Once your mail lands, the next question is who to send it to. Read buying signals in B2B sales.
New to the research side? Start with what sales prospecting is.