Cold email, defined plainly.

The share of sent emails that come back undelivered. A hard bounce is permanent: the address does not exist or the domain refuses mail, and it should never be emailed again. A soft bounce is temporary, such as a full mailbox or a server that is briefly unavailable, and may clear on a later attempt. Inbox providers read a rising hard bounce rate as a sign of a careless list, so it damages sender reputation quickly.

Lead verificationSender reputationCatch-all addressHow we verify every lead

An address at a domain whose mail server accepts messages for any name, real or not. Because the server says yes to everything, a verification tool cannot confirm whether a specific person's mailbox exists, so the result comes back as unknown rather than valid. Mail to a catch-all may be delivered, silently discarded or bounced later. Careful senders either remove catch-all addresses or send to them in small, separately watched batches.

Lead verificationBounce rateLead sourcing and verification

The ability of your email to reach the inbox rather than spam, the promotions tab or nowhere at all. Delivery only means the receiving server accepted the message; deliverability is about where it then lands. It depends on authentication, sender reputation, list quality, sending volume, content and how recipients respond. For cold email it is the first thing to get right, because copy that lands in spam is never read.

Inbox placementSender reputationWarmupCold email deliverability in 2026

DomainKeys Identified Mail. The sending server signs each message with a private key, and publishes the matching public key in a DNS record on the sending domain. The receiving server uses that key to check the signature, which proves the message really came from that domain and was not altered on the way. Missing or broken DKIM is one of the fastest ways to land in spam with Google and Microsoft.

SPFDMARCSending domainDomain and mailbox setup

Domain-based Message Authentication, Reporting and Conformance. A DNS record that tells receiving servers what to do when a message fails SPF and DKIM checks or does not align with the visible From domain: deliver it anyway, quarantine it or reject it. It also asks receivers to send reports on the mail they saw from your domain. Major inbox providers now expect bulk senders to publish a DMARC record.

SPFDKIMDeliverabilityDomain and mailbox setup

Any email in a sequence after the first, sent to someone who has not replied. A good follow-up adds something new, such as a different angle, a short example or a simpler question, rather than asking whether the last message was seen. Follow-ups must stop the moment a person replies or opts out. Many replies arrive on a later step, which is why a single email is rarely a fair test of an offer.

SequenceReply rateSequence writing

A description of the companies most likely to buy from you and the people inside them who sign: industry, company size, location, the tools they use and the title of the buyer. The strongest profiles come from looking at deals you have already closed rather than from guesses. In cold email the ICP decides who goes on the list, and a list that misses it cannot be fixed by better copy.

Lead verificationReply rateHow we build a list from your ICP

Where a delivered email actually ends up: the primary inbox, a secondary tab or the spam folder. It is measured with seed tests, which send to a panel of test mailboxes at different providers and record where each copy landed. Placement can differ between Gmail and Outlook for the same message, and it can change from week to week, so it is worth checking before launch and while a campaign runs.

DeliverabilitySender reputationWarmupLaunch and monitoring

Checking that each email address on a list can receive mail before anything is sent to it. Verification tools test the syntax, look up the domain's mail servers and ask the server whether the mailbox exists, without delivering a message. Results come back as valid, invalid, risky or unknown. Running two independent providers and removing anything not clearly valid keeps the bounce rate low and protects new sending domains.

Bounce rateCatch-all addressICP (ideal customer profile)Lead sourcing and verification

A domain registered for sending cold email that closely resembles your main one, such as getacme.com or tryacme.com alongside acme.com. Recipients still recognise the brand, but any damage to reputation stays on the lookalike rather than the domain your team uses for everyday mail. A lookalike usually redirects to your main website and needs its own SPF, DKIM, DMARC and warmup before it sends.

Sending domainSender reputationWarmupLookalike domains for cold email

Spreading a campaign's sends across several mailboxes and domains instead of sending everything from one address. Each mailbox stays within a modest daily volume, so no single sender looks like a bulk mailer, and if one mailbox shows trouble it can be paused while the others carry on. Rotation is how a campaign reaches thousands of emails a month without pushing any one inbox past what providers tolerate.

Sending domainSender reputationDeliverabilityCold emails per day per mailbox

Counting opens by placing a tiny invisible image in each email and logging when it loads. The number is unreliable. Apple Mail Privacy Protection loads images automatically, which records opens that never happened, while clients that block images hide real ones. The tracking pixel and its link can also count against the message with spam filters. Replies are a far more honest measure of whether a cold email worked.

Reply rateDeliverabilityReply rate benchmarks

Replies received divided by the number of people contacted, usually counted per lead across the whole sequence rather than per email. It is the metric that matters most in cold email, though not every reply is positive: some are referrals, objections or requests to stop. Published benchmarks rarely say how they counted, so the useful comparison is your own campaign against itself as the list, offer and copy change.

Open trackingFollow-upICP (ideal customer profile)Reply rate benchmarks by industry

The trust an inbox provider assigns to a sending domain and its mailboxes, built from their history. Replies, low bounce rates, few spam complaints and steady volume raise it; sudden spikes, invalid addresses and complaints lower it. Providers use it to decide whether a message reaches the inbox. New domains start with no reputation at all, which is why they need warmup before they send cold email.

WarmupSpam complaint rateBounce rateCold email deliverability in 2026

The domain that appears after the @ in the From address and that receiving servers authenticate. For cold email it should not be the domain your company uses every day, so outbound volume never puts invoices, support mail or internal messages at risk. Sending domains are usually lookalikes, each set up with its own mailboxes, SPF, DKIM and DMARC, and each warmed before it carries a campaign.

Lookalike domainDKIMMailbox rotationDomain and mailbox setup

The ordered set of emails a prospect receives in a cold campaign, with a set number of days between each step. The first email introduces the reason for writing; later steps follow up with a new angle. A sending tool runs the sequence automatically and stops it for anyone who replies, bounces or opts out. Short emails with a single clear ask tend to read better than long ones.

Follow-upReply rateSequence writing

The share of recipients who mark a message as spam. Google asks bulk senders to keep it below 0.3 percent and ideally under 0.1 percent, and complaints weigh more heavily against a sender than almost any other signal. In cold email the rate stays low when the list matches the ICP, the copy is relevant and unsubscribing is easier than reaching for the spam button.

Sender reputationUnsubscribe header (List-Unsubscribe)ICP (ideal customer profile)Cold email deliverability checklist

Sender Policy Framework. A DNS record on the sending domain that lists the servers allowed to send mail on its behalf, such as Google Workspace or Microsoft 365. The receiving server compares the connecting server against that list and treats unlisted senders with suspicion. A domain should have exactly one SPF record, and it works alongside DKIM and DMARC rather than replacing them.

DKIMDMARCSending domainDomain and mailbox setup

An email header that lets the recipient's mail client show its own unsubscribe button next to the sender's name. The one-click version, defined in RFC 8058, lets people opt out with a single click and no further pages. Gmail and Yahoo require one-click unsubscribe from bulk senders. Even below those thresholds it is worth including, because an easy opt-out is far better than a spam complaint.

Spam complaint rateDeliverabilityThe rules we work by

The period in which a new mailbox sends small, gradually rising volumes of mail that gets opened, replied to and rescued from spam, so inbox providers can build a history for it. A mailbox that sends cold email with no history looks like a spammer and is filtered as one. Warmup cannot be rushed: we run it for at least fourteen days before any campaign launches.

Sender reputationInbox placementLookalike domainWhy 14 days is the minimum