bouncelens-email-check (Clojure)

Clojure library that checks email addresses before you send to them or save them:

• Typos in the domain: jane@gmial.com → did you mean jane@gmail.com?
• Disposable / throwaway domains (~9,000 built in)
• Dead domains: the domain doesn't exist, has no mail server, or accepts no email (null MX)
• Bad syntax, role addresses (info@, sales@), free providers, duplicates (Gmail dot and +tag variants count as the same inbox)
• The mail provider behind the domain (Google, Microsoft, Proofpoint, …)

No API key, no account. It's the Clojure version of the free checker at bouncelens.com and returns the same results.

It never connects to the recipient's mail server, so it can't confirm that a mailbox exists. The best status is :unconfirmed (format and domain OK).

Install

;; deps.edn
net.clojars.akshaycu777/bouncelens-email-check {:mvn/version "1.0.0"}
;; Leiningen
[net.clojars.akshaycu777/bouncelens-email-check "1.0.0"]

Use

(require '[bouncelens.email-check :as ec])

(ec/check-one "jane@gmial.com")
;; => {:status :risky, :did-you-mean "jane@gmail.com",
;;     :reasons ["..." "Looks like a typo of gmail.com"], :flags {...}, ...}

(def results (ec/check ["jane@gmail.com" "temp@mailinator.com" "Jane@Gmail.com"]))
(ec/summarize results)
;; => {:total 3, :unconfirmed 1, :risky 1, :duplicates 1, ...}

:status	Meaning
:invalid	Will bounce: bad syntax, domain doesn't exist, no mail server, or null MX
:risky	Disposable domain, likely typo, no MX record, non-English characters before @, or the DNS lookup failed
:unconfirmed	Format and domain OK. The mailbox itself isn't checked

Options for check: :concurrency (domains looked up at once, default 8), :disposable (your own set), :lookup ((fn [domain] -> info), e.g. a cached resolver).

Each unique domain is looked up once per call. Only the domain is sent to Cloudflare's DNS-over-HTTPS resolver (1.1.1.1). Requires Java 11+.

Tests

lein test

Offline: test-resources/dns.json holds recorded DNS answers and golden.json the BounceLens JavaScript engine's results for the same inputs; the Clojure code must match them exactly.

More from BounceLens

• bouncelens.com – free email list checker in your browser
• Go library + self-hosted API (also on Docker Hub)
• MCP server for AI agents

License

MIT. Disposable-domain list: disposable-email-domains (CC0).