Cold Email Glossary

Sending Domain

A dedicated domain used exclusively for cold outreach, completely separate from the main business domain. Isolates any deliverability risk from the primary domain's reputation.

Inbox Warm-Up

The process of gradually increasing sending volume from a new inbox by exchanging emails with a warm-up network. Builds positive sending history before cold outreach begins. Minimum three to four weeks before first campaign sends.

SPF (Sender Policy Framework)

A DNS authentication record that specifies which mail servers are authorised to send email on behalf of a domain. Missing or incorrect SPF is a common cause of deliverability failures.

DKIM (DomainKeys Identified Mail)

A DNS authentication record that adds a cryptographic signature to outgoing emails, allowing receiving servers to verify the message was not tampered with in transit.

DMARC

A DNS policy record that tells receiving mail servers what to do when SPF or DKIM checks fail. Options are none, quarantine (send to spam), or reject. Required for bulk senders by Google and Yahoo since February 2024.

Inbox Placement Rate

The percentage of sent emails that land in the recipient's primary inbox rather than spam or promotions. The most meaningful deliverability metric for cold email, more important than delivery rate alone.

Sender Reputation

A score assigned by email providers to a sending domain and IP based on engagement history, spam complaint rate, bounce rate, and authentication. Low sender reputation is the primary cause of inbox placement failure.

Spam Complaint Rate

The percentage of recipients who mark a message as spam. Google and Yahoo require this to stay below 0.3 percent (3 complaints per 1,000 sends). Exceeding this threshold triggers deliverability penalties.

Blacklist

A publicly maintained list of domains or IP addresses identified as sources of spam. Inclusion causes emails to be blocked or routed to spam across all receiving servers that check the list. Spamhaus and Barracuda are the most commonly checked blacklists in B2B.

Inbox Rotation

The practice of distributing campaign sends across multiple warmed inboxes rather than sending all volume from a single inbox. Keeps individual inbox send volumes low and protects sender reputation during high-volume campaigns.

Email Validation

The process of checking whether an email address exists, is active, and is safe to send to before it enters a campaign. High bounce rates from unvalidated lists damage sender reputation rapidly, particularly on new domains.

Hard Bounce

A permanent delivery failure because the email address does not exist or the domain is invalid. Hard bounces should be removed from the list immediately and never retried.

Soft Bounce

A temporary delivery failure caused by a full mailbox, server outage, or message size limit. Unlike hard bounces, soft bounces can be retried, though repeated soft bounces on the same address indicate a problem worth investigating.

Catch-All Domain

A domain configured to accept every email sent to it regardless of whether the specific mailbox exists. Standard validation tools return positive results for catch-all addresses even if the contact email is not real. Requires specialist tools to assess actual delivery likelihood.

Data Decay

The rate at which contact data becomes outdated as people change roles, companies, or email addresses. B2B contact data decays at roughly 20 to 25 percent per year. Lists older than six months should be re-validated before use.

Cold Email Sequence

A pre-built series of emails sent to a prospect over a set number of days, with defined intervals between each step. Most B2B sequences run three to five steps with two to four days between touches.

Subsequence

A separate follow-up sequence triggered by a specific prospect behaviour, such as opening an email without replying. Replaces generic follow-ups with a message tailored to the prospect's engagement level.

Step Interval

The number of days between each email in a sequence. Too short feels aggressive and increases unsubscribes. Too long loses momentum. Three to five days between steps is the standard for most B2B cold email campaigns.

Personalisation Variable

A dynamic field in an email template that pulls contact-specific data such as first name, company name, job title, or a custom research note. Basic first-name personalisation alone does not move reply rates. Role-relevant and pain-specific personalisation does.

Plain Text Email

An email formatted without HTML, images, or styling, sent to appear as a standard message from one person to another. Performs better in cold outreach than HTML emails because it avoids formatting signals that trigger spam filters.

Subject Line Test

A structured comparison of two or more subject lines sent to equal segments of a list to identify which drives higher open rates before rolling out to the full campaign volume.

Call to Action (CTA)

The single action the email asks the prospect to take. In cold email, effective CTAs are low-friction: a yes/no question, a request for the right person, or an invitation to see one piece of information. A meeting request as a first CTA consistently underperforms softer alternatives.

Break-Up Email

The final email in a cold sequence, explicitly acknowledging it is the last contact attempt. Often outperforms earlier steps in the sequence because it creates a sense of finality that prompts replies from prospects who were interested but had not yet responded.

Open Rate

The percentage of delivered emails that are opened by the recipient. Used as a deliverability and subject line signal rather than a conversion metric. Open tracking via pixel is increasingly unreliable due to Apple Mail Privacy Protection and corporate email proxies pre-loading images.

Reply Rate

The percentage of sent emails that receive any reply, positive or negative. The primary engagement metric for cold email. A well-targeted B2B cold email campaign achieves 8 to 15 percent reply rate. Industry-wide averages across all targeting quality run 1 to 5 percent.

Positive Reply Rate

The percentage of replies that indicate genuine interest, such as a request for more information, a meeting acceptance, or a referral to the right contact. Separates signal from noise in campaign performance reporting.

Open Depth

The number of times a single email is opened by the same recipient. Multiple opens from the same contact within a short window indicate strong interest and can be used to prioritise follow-up timing or trigger a calling step in a multichannel sequence.

Bounce Rate

The percentage of sent emails that could not be delivered. Hard bounces above 2 percent on a new domain can trigger deliverability penalties. Keeping bounce rate below 1 percent is the standard target for well-validated cold email lists.