Short definitions of the terms used across Outbound Atlas. Each entry links to the page that explains the term in context. Figures and dated rules live on the linked pages, not here, because they change monthly in this market. Where vendors use different names for the same thing (Unibox, Master Inbox), both appear.
A
A/B testing (A/Z testing). Splitting leads across copy variants and declaring a winner; "A/Z" is Instantly's name for testing more than two variants. None of the leaders documents significance testing. A/B testing
Abmahnung. A German cease-and-desist letter, usually with a fee claim, sent by a recipient, competitor or association after an unlawful marketing email. It is the main enforcement route against cold email in Germany, and costs rise sharply if sending continues. Germany
AI campaign builder. A feature where the user describes the target and offer and the AI picks leads, writes the sequence and launches it, increasingly exposed as MCP tools inside Claude or ChatGPT. AI campaign builder
AI personalisation. LLM-written first lines or whole emails generated per lead, usually billed in credits. AI personalisation
AI reply agent. An LLM that classifies inbound replies and drafts or sends responses, either after human approval (HITL) or fully automatically (Autopilot). AI reply agent
AI SDR. Software sold as a replacement for a sales development rep: it finds leads, writes and sends outreach and handles replies end to end. Examples are 11x, Artisan and AiSDR. AI SDR layer
AirMail. Instantly's own hosted inboxes on its own servers, launched as an alternative to resold Google and Microsoft accounts. Instantly
App password. A mailbox-specific password that lets a third-party tool log in over IMAP/SMTP without OAuth. Google still allows it as the exception to its less-secure-apps shutdown. OAuth verification and the end of basic auth
ARR (annual recurring revenue). Recurring revenue run-rate. In this market most ARR figures are founder claims or third-party estimates (GetLatka, Sacra), and the hub labels them as such. Market size
Art. 13(5) ePrivacy. The clause letting each EU member state decide whether legal persons (companies) get the same opt-in protection as individuals. It is why B2B cold email is legal in France and not in Germany. EU/EEA country matrix
Art. 14 notice. The GDPR duty to tell people whose data you did not collect from them who you are, what you hold and where you got it. Data vendors and cold senders often skip it; the CNIL fined KASPR partly for this. Data sourcing law
Art. 21 objection. A person's GDPR right to object to direct marketing. It is unconditional, so a "stop" must suppress the contact everywhere. GDPR and ePrivacy
B
BIMI. A DNS standard that shows a brand logo next to authenticated mail at some providers. It needs strict DMARC and usually a paid certificate, so it is irrelevant to cold sending domains. Authentication: SPF, DKIM, DMARC, BIMI, ARC and one-click unsubscribe
Blocklist. A public or private list of IPs or domains flagged for spam (Spamhaus is the best known). Listing can block mail at many receivers at once. Reputation and blocklists
Bounce (hard and soft). A delivery failure. A hard bounce is permanent (address does not exist); a soft bounce is temporary (mailbox full, throttled). High hard-bounce rates burn mailboxes fast. Bounce protection
Bounce protection. Automatically pausing sending when bounces cross a threshold. The leaders do it per campaign; per-mailbox, rolling-window protection is rare. Bounce protection
Bring your own inboxes. The model where customers buy their own Google or Microsoft mailboxes and connect them to the sequencer. The sequencer carries no infrastructure risk but earns no inbox margin. Infrastructure strategy: build or partner
Bulk sender. Gmail's and Yahoo's category for domains sending above a daily volume threshold to personal mailboxes; bulk senders must meet stricter authentication, unsubscribe and complaint rules. Most cold domains never reach it. Google and Yahoo sender rules
C
CAN-SPAM. The US federal commercial-email law. It allows cold B2B email without consent but requires honest headers and subject lines, a physical address and a working opt-out. United States: CAN-SPAM and state email laws
CASA. Google's Cloud Application Security Assessment, an annual third-party security audit required for apps that use restricted Gmail scopes. Levels are now called AL1 and AL2. OAuth verification and the end of basic auth
CASL. Canada's Anti-Spam Legislation: opt-in, with narrow implied-consent exceptions. Canada: CASL
CASL implied consent (conspicuous publication). The CASL route for cold B2B email: the address was conspicuously published, carried no "no unsolicited messages" notice, and the message is relevant to the person's role. The sender must prove all three per message. Canada: CASL
Catch-all domain. A domain whose mail server accepts mail for any address, so standard SMTP verification cannot tell valid from invalid addresses. Catch-all verification is the one part of verification that still commands a price. Email verification
Client workspace. A separate, isolated account area for each agency client, with its own mailboxes, campaigns and users. Some vendors charge per workspace. Workspaces, roles and SSO
Complaint rate (spam rate). The share of delivered mail that recipients mark as spam, as measured by the mailbox provider. Gmail publishes thresholds for personal mailboxes; Microsoft does not. Google and Yahoo sender rules
Conditional sequence. A sequence that branches on what a lead did (replied, clicked, accepted a LinkedIn request) or what they said. Conditional sequences and subsequences
Controller and processor. GDPR roles. The controller decides why and how personal data is used; the processor acts on its instructions. A sequencer is usually a processor for customers' campaign data and becomes a controller when it sells its own database. Platform liability: what the sequencer itself risks
Corporate subscriber. Under UK PECR, a company, LLP, Scottish partnership or public body, which can be emailed without prior consent if the sender identifies itself and offers an opt-out. UK: PECR and DUAA 2025
Credits. The metering unit for data lookups, verification and AI actions inside sequencers and data tools. Credits are where much of the new revenue in this market comes from. Business models
CRM sync. Pushing replies, interested leads and activity from the sequencer into HubSpot, Salesforce or Pipedrive. CRM sync
D
Dedicated IP. A sending IP used by one customer only, so its reputation is not shared with others. Mostly relevant to private-SMTP infrastructure. Google vs Microsoft vs SMTP
DFY inboxes (done-for-you). Mailboxes, domains and DNS set up by the vendor and sold ready to send, often pre-warmed. Instantly, Smartlead and the infra resellers all sell them. Inbox & domain infrastructure
Digital Omnibus. The European Commission's package of proposed amendments to the GDPR and other digital rules. Its effect on B2B marketing is still open. GDPR and ePrivacy
DKIM. A cryptographic signature in the mail header that proves the message was authorised by the signing domain and not altered. Authentication: SPF, DKIM, DMARC, BIMI, ARC and one-click unsubscribe
DMARC. A DNS policy that tells receivers what to do when SPF or DKIM fails for a domain, and where to send reports. Authentication: SPF, DKIM, DMARC, BIMI, ARC and one-click unsubscribe
DMARC alignment. The DMARC requirement that the domain in the visible From address matches the domain authenticated by SPF or DKIM. Authentication without alignment does not satisfy DMARC. Authentication: SPF, DKIM, DMARC, BIMI, ARC and one-click unsubscribe
Domain reputation. The mailbox provider's view of a sending domain's history, built from complaints, engagement and authentication. For cold email it matters more than IP reputation. Reputation and blocklists
DSA (Digital Services Act). The EU law governing online intermediaries. Whether and how it applies to a cold-email SaaS is unsettled. Platform liability: what the sequencer itself risks
DUAA (Data (Use and Access) Act 2025). The UK law that raised PECR fines to the GDPR-level maximum and amended direct-marketing rules. UK: PECR and DUAA 2025
E
Email finder. A tool that guesses and checks a person's work email from their name and company domain. Contact data and enrichment
ePrivacy Directive. The EU directive that decides whether you may send electronic marketing at all; the GDPR then governs how you hold the contact data. The planned ePrivacy Regulation was withdrawn. GDPR and ePrivacy
ESP. Strictly an email service provider (SendGrid, Mailgun, SES). In cold email the term is loosely used for the mailbox provider (Google, Microsoft), as in "ESP matching". Provider rules: Google, Microsoft and the ESPs
ESP matching. Sending to Gmail recipients from Google mailboxes and to Outlook recipients from Microsoft mailboxes, on the theory that same-provider mail lands better. Its impact numbers are unaudited. ESP matching
G
GetLatka. A database of SaaS revenue and headcount figures, partly self-reported in founder interviews and partly estimated. The hub treats its numbers as estimates with wide error bars. Market size
Google Workspace mailbox. A paid Google business mailbox, the most trusted and most expensive sending option, and the one most exposed to Google's 2025 suspensions. Google vs Microsoft vs SMTP
GTM engineer. A go-to-market role that builds outbound as a data pipeline, usually in Clay, and treats the sequencer as a headless sending endpoint chosen on API and webhook coverage. GTM engineers
H
Headless sending. Using a sequencer or infra provider through its API only, with the user interface and logic living elsewhere (Clay, n8n, an AI agent). Sending engine as an API
HITL (human in the loop). An AI mode where a person approves each AI-drafted reply or message before it is sent. AI reply agent
I
Inbox placement. Whether a delivered message lands in the inbox, a secondary tab or spam. Delivery rate and placement are different numbers. Inbox placement testing
Inbox rotation. Spreading one campaign across many sending mailboxes so each stays under a safe daily cap. It is the mechanical core of the volume model. Inbox rotation
Inferred consent. The Australian and New Zealand route for cold B2B email: the address was conspicuously published and the message relates to the person's role. Australia, New Zealand and APAC
Infra reseller. A vendor that sells Google, Microsoft or private-SMTP mailboxes to cold senders, often with domains and DNS included. Zapmail, Mailforge, Maildoso and Scaledmail are examples. Inbox & domain infrastructure
Initiator. Under CAN-SPAM, whoever originates or pays someone else to send a commercial email. The client who pays an agency is an initiator; a platform that only transmits is not. United States: CAN-SPAM and state email laws
Intent data. Signals that an account is researching a topic, such as content consumption tracked by Bombora or G2. Signals layer
Inteligo Media (C-654/23). A November 2025 CJEU ruling that, where ePrivacy Art. 13 applies to email marketing, it is the special rule and no separate GDPR Art. 6 basis is needed for the sending. GDPR and ePrivacy
J
JMRP. Microsoft's Junk Mail Reporting Program, a feedback loop that passes complaint reports to IP owners. It was changed alongside SNDS in June 2026. Microsoft rules: Outlook.com and Microsoft 365 limits
L
Lead database. Contact data sold inside the sequencer on credits. Every volume tool now has one. Built-in lead database
Legitimate interest. The GDPR legal basis (Art. 6(1)(f)) most B2B contact databases rely on. It requires a balancing test, notices and respect for objections. Data sourcing law
lemwarm. lemlist's warmup product, once given away free as a growth wedge. Warmup networks
LinkedIn automation. Tools that send connection requests, messages and profile visits from LinkedIn accounts at scale, against LinkedIn's terms. HeyReach and Expandi are examples. Multichannel: LinkedIn, calls, SMS and video
List-Unsubscribe header. A mail header that gives the recipient's mail client an unsubscribe action. Combined with RFC 8058 it enables one-click unsubscribe. Authentication: SPF, DKIM, DMARC, BIMI, ARC and one-click unsubscribe
llms.txt. A plain-text file on a vendor's site written for AI agents, describing the product and pricing. Instantly and Smartlead both publish one. Instantly
M
MCP (Model Context Protocol). A standard that lets AI assistants call a product's functions as "tools". Instantly, Smartlead, lemlist and Apollo all ship official MCP servers. API, webhooks and MCP
Meeting rate. Meetings booked per lead contacted. Almost nobody publishes it with a stated method. Reply benchmarks
MERRL. Microsoft's proposed per-mailbox external recipient rate limit. It was reported cancelled in January 2026. Microsoft rules: Outlook.com and Microsoft 365 limits
Microsoft 365 tenant. A Microsoft business account that can host many mailboxes on many domains. Resellers sell tenant-based mailboxes in bulk. Google vs Microsoft vs SMTP
MPP (Apple Mail Privacy Protection). Apple's feature that pre-loads images, including tracking pixels, so opens are recorded whether or not a person read the email. It is one reason open rates are noise. Content and tracking
Multichannel steps. LinkedIn, call, SMS or WhatsApp steps inside an email sequence. Multichannel steps
MX record. The DNS record naming the mail server for a domain. ESP matching reads it to decide whether a recipient is on Google or Microsoft. ESP matching
O
OAuth. The token-based login that lets an app access a mailbox without storing the password. For Gmail, reading mail needs restricted scopes and therefore CASA. OAuth verification and the end of basic auth
onmicrosoft.com domain. The default domain every Microsoft 365 tenant gets. Microsoft caps external mail from it at a very low daily volume. Provider crackdowns
One-click unsubscribe. An unsubscribe that works with a single action from the mail client, without a login or confirmation page, defined in RFC 8058. Gmail and Yahoo require it from bulk senders. Authentication: SPF, DKIM, DMARC, BIMI, ARC and one-click unsubscribe
Open tracking. Counting opens through a hidden pixel. MPP, security scanners and image caching have made it unreliable. Content and tracking
Opt-in and opt-out regimes. Opt-in law requires consent before the first marketing email; opt-out law allows the first email if the recipient can stop further ones. Cold email law: the jurisdiction matrix
P
Panel accounts. Bulk Google accounts carved out of education, nonprofit or legacy G Suite programmes and resold to cold senders. They were the main target of Google's autumn 2025 suspensions. Provider crackdowns
Pay-per-meeting. An agency pricing model where the client pays per booked meeting rather than a retainer. Published prices are scarce. Lead-gen agencies
PECR. The UK Privacy and Electronic Communications Regulations, the UK's ePrivacy implementation. B2B email to corporate subscribers is opt-out. UK: PECR and DUAA 2025
Placement test. Sending a test message to a seed list of monitored mailboxes to see where it lands. Useful, but blind to how real recipients' filters treat you. Inbox placement testing
Positive reply rate. Interested replies divided by leads or emails sent. It excludes auto-replies, out-of-office notices and "remove me". No vendor publishes how it classifies replies, so cross-tool comparisons are unreliable. Reply benchmarks
Postmaster Tools. Google's dashboard for senders to personal Gmail. Version 2 shows compliance, spam rate and errors; the domain and IP reputation dashboards of version 1 were retired. Reputation and blocklists
Pre-warmed inboxes. Mailboxes sold after a warmup period so they can send at full volume on day one. Inbox & domain infrastructure
Premium and private warmup pools. Paid tiers of a warmup network with older or more trusted accounts, sold by Instantly and others as an upsell over the standard pool. Built-in warmup
Presumed consent (Germany). Under §7 UWG, a business may be phoned if there is a concrete reason to think it would welcome the call. It does not apply to email. Germany
Primary domain. The company's main domain (its website and staff email). Cold senders keep it out of cold campaigns to protect its reputation. See sending domain. In-house SDR teams
Private SMTP. Mailboxes on servers run by a reseller rather than Google or Microsoft. It is the cheapest option and the least trusted by receivers. Google vs Microsoft vs SMTP
PTR record (reverse DNS). A DNS record mapping an IP address back to a hostname. Gmail requires matching forward and reverse DNS from all senders. Google and Yahoo sender rules
R
Ramp. Raising a new mailbox's daily volume gradually over weeks. Practitioners agree on ramping even when they disagree about warmup pools. Does warmup work?
Reply rate. Replies divided by emails sent or delivered. Published averages differ by an order of magnitude because the denominators differ. Reply benchmarks
Restricted scope. A Gmail API permission that Google classifies as high-risk, such as reading mail. Using one requires verification and an annual CASA assessment. OAuth verification and the end of basic auth
RFC 8058. The standard for one-click unsubscribe via a List-Unsubscribe-Post header. Required by Gmail and Yahoo for bulk senders; legally ambiguous but cheap insurance for cold email. Authentication: SPF, DKIM, DMARC, BIMI, ARC and one-click unsubscribe
Routine conveyance. The CAN-SPAM carve-out for transmitting, routing or storing mail through an automatic technical process. It keeps a pure sending platform from being treated as the initiator. United States: CAN-SPAM and state email laws
S
SEG (secure email gateway). A filter such as Proofpoint or Mimecast that sits in front of a company's mailboxes and screens inbound mail before Google or Microsoft see it. How filtering works
Sending domain. A separate, look-alike domain bought only to send cold email, so damage to its reputation does not reach the primary domain. Also called a secondary domain. Reputation and blocklists
Sending limits. Per-mailbox daily caps, campaign caps, ramps and gaps between sends that keep volume under what providers tolerate. Sending limits and throttling
Sequencer. Software that sends a series of emails (and sometimes other steps) to a list on a schedule and stops when someone replies. Sequencing & sending
Signals. Events that suggest when to contact whom: intent data, job changes, funding, website visits. Signals layer
SMTP AUTH. Password-based authentication to submit mail over SMTP. Microsoft is switching Basic SMTP AUTH off by default for Exchange Online tenants. OAuth verification and the end of basic auth
SNDS. Microsoft's Smart Network Data Services, an IP-based dashboard of sending data and complaints. It shows nothing for senders on shared Microsoft 365 or Google infrastructure. Microsoft rules: Outlook.com and Microsoft 365 limits
Soft opt-in. The UK and EU exception that lets a business email existing customers about similar products without fresh consent. It does not cover cold prospects. UK: PECR and DUAA 2025
Sole trader. Under PECR, a self-employed individual or certain partnerships, treated as an individual subscriber, so the consent rule applies even to their business address. UK: PECR and DUAA 2025
Spintax. Inline syntax such as {Hi|Hello|Hey} that randomises wording so no two emails are byte-identical. It is being overtaken by AI-written copy. Spintax and message variants
SPF. A DNS record listing the servers allowed to send mail for a domain. Authentication: SPF, DKIM, DMARC, BIMI, ARC and one-click unsubscribe
SSO. Single sign-on through a company identity provider. Procurement asks for it; volume tools rarely document it. Workspaces, roles and SSO
Störerhaftung. German "interferer liability", under which someone who contributes to another's unlawful act can be ordered to stop it. Its application to a cold-email platform is untested. Germany
Subsequence. A follow-up branch triggered by a lead's reply or action, as Instantly calls it. Conditional sequences and subsequences
Suppression list. Addresses and domains that must never be emailed again, such as unsubscribes, objections and bounces. It must work across campaigns and workspaces. Sending architecture
T
TERRL. Microsoft's tenant external recipient rate limit, a tenant-wide daily cap that grows with the number of licences. Trial tenants have a lower cap. Microsoft rules: Outlook.com and Microsoft 365 limits
Tracking domain. A custom domain (via CNAME) used for the open pixel and click redirects instead of the vendor's shared tracking domain. Custom tracking domains
U
Unibox. Instantly's name for a unified inbox that collects replies from every connected sending mailbox in one view. Smartlead calls it Master Inbox. Unified inbox (Unibox)
Unlimited inboxes. The flat-fee pricing model, popularised by Instantly, where customers connect as many sending mailboxes as they like and pay by contacts or emails. Business models
UWG §7. The German Act against Unfair Competition provision that bans marketing email without prior express consent, B2B included. Recipients and competitors enforce it through Abmahnungen. Germany
V
Verification. Checking an address with the receiving server before sending, to keep bounces low. It is increasingly bundled free. Email verification
Visitor identification. Matching anonymous website visitors to companies or people. Person-level tools such as RB2B work only on US traffic, and person-level identification is legally risky in the EU. Signals layer
Volume sequencer. A sequencer built for many mailboxes and high daily volume at a flat fee, such as Instantly, Smartlead, EmailBison and PlusVibe. Sequencing & sending
W
Warmup. Building a new mailbox's reputation before cold sending, either by ramping real volume or by joining a warmup pool. Built-in warmup
Warmup pool. A peer-to-peer network of mailboxes that send, open, rescue from spam and reply to each other automatically to simulate engagement. It is bundled free by every volume tool, and filters may discount or punish it. Warmup networks
Waterfall enrichment. Querying several data providers in sequence until one returns a verified email or phone number, paying only for hits. Clay popularised it; Instantly and others now build it in. Contact data and enrichment
Webhook. An HTTP callback the sequencer fires when an event happens, such as a reply, bounce or unsubscribe. GTM engineers choose tools on webhook coverage. API, webhooks and MCP
White-label. Rebranding the sequencer with an agency's logo and domain so its clients log in to "the agency's" tool. It is priced per client at some vendors and built in at others. White-label and agency portals