# Block free email domains on B2B forms: the 4,768-domain list and a free API By Steven Van · 2026-10-10 The free email check API costs 0 credits per call and applies HubSpot's 4,768-domain list to signups, lead lists and agents, with caveats on where it misfires. HubSpot's "Block free email providers" form setting rejects free addresses using a published list of 4,768 domains. [Unif Cookbooks]() has turned that list into a free API in [Unif API](), so the same rule can run outside HubSpot forms, in signup code, CRM cleanup jobs and AI agents. ## Four ways to apply the rule - **GET /email/check** for a form or signup handler. It checks one address and returns a verdict. - **POST /email/check/batch** for lead lists or CRM exports. It takes up to 1,000 addresses per call and returns results in input order, duplicates included. - **GET /email/domains/{domain}** for a company domain column. It accepts a domain, address or URL. - **GET /email/free-domains**, or the npm package, to sync the list and run it offline. All four endpoints cost **0 credits** per call, and a workspace with a zero balance can call them. They run without network lookups. The response has a verdict field of business, free or invalid. For invalid addresses, invalid\_reason gives missing\_at\_sign, invalid\_local\_part, invalid\_domain or too\_long. Role mailboxes such as info@ and sales@ are flagged separately. ## Offline and no-code options The open-source, zero-dependency package @unifapi/email-filter exposes checkEmail. It runs in Node, edge runtimes and the browser, and ships the raw list as JSON and plain text. The snapshot date is exported as FREE\_EMAIL\_DOMAINS\_SNAPSHOT\_DATE. A browser-based checker runs the same package on up to 10,000 pasted addresses or domains, splits them into business, free provider and invalid, flags role mailboxes, removes duplicates and exports a CSV. Nothing pasted is uploaded. With Unif API connected over MCP, an agent can run the batch endpoint itself, for example to classify a webinar sign-up export before spending credits on enrichment. ## What the list contains Unif analysed the October 10, 2026 snapshot of HubSpot's CSV. It is not affiliated with HubSpot. The list covers global webmail (gmail.com, yahoo.com, outlook.com), country variants (51 yahoo.\*, 33 outlook.\*, 24 live.\* and 22 hotmail.\* domains), regional providers, ISP mailboxes, privacy-focused providers and some disposable inboxes. 1,264 of the entries are legacy mail2\*.com vanity domains, so the total overstates how much current personal email it covers. ## Where blocking misfires - Real buyers, such as founders and consultants, use personal addresses. - ISP and privacy mailboxes (comcast.net, protonmail.com) are blocked, though their owners may not be consumers. - Newer providers such as proton.me, pm.me, tuta.com and hey.com are not listed, and neither is guerrillamail.com, so it is not a full disposable-email list. - A non-listed domain can still be a typo, a parked domain or a bouncing mailbox. Nothing checks MX records. - Matching is exact, so berlin.de is listed but senate.berlin.de is not treated as free. Unif suggests routing rather than blocking: send free-domain signups to a self-serve or nurture path, ask for a company name, and keep sales follow-up for business domains. ![Unif API]() Unif API Prebuilt AI marketing agents for SEO, GEO, influencer research, social listening, and competitor analysis — run them inside Claude, ChatGPT, or Codex over one MCP server. [View Unif API →]() Sources [Original source]() [Read Block free email domains on B2B forms: the 4,768-domain list and a free API on Creators Toolbox]() --- Canonical source: https://creatorstoolbox.com/blog/unif-api-block-free-email-domains-on-b2b-forms-the-4-768-domain-list-and-a-free