created_at2019-10-21 10:17:38.180812
updated_at2023-10-10 19:06:30.623981
descriptionCheck if an email address exists without sending any email
Amaury (amaurym)



Crate Docs Docker Actions Status



Check if an email address exists without sending any email.
Comes with a ⚙️ HTTP backend.

👉 Live Demo:

This is open-source, but I also offer a SaaS solution that has check-if-email-exists packaged in a nice friendly web interface. If you are interested, find out more at Reacher. If you have any questions, you can contact me at

Get Started

3 non-SaaS ways to get started with check-if-email-exists.

1. ⚙️ HTTP backend using Docker (popular method 🥇) [Full docs]

This option allows you to run a HTTP backend using Docker 🐳, on a cloud instance or your own server. Please note that outbound port 25 must be open.

docker run -p 8080:8080 reacherhq/backend:latest

Then send a POST http://localhost:8080/v0/check_email request with the following body:

    "to_email": "",
    "from_email": "", // (optional) email to use in the `FROM` SMTP command, defaults to ""
    "hello_name": "",    // (optional) name to use in the `EHLO` SMTP command, defaults to "localhost"
    "proxy": {                        // (optional) SOCK5 proxy to run the verification through, default is empty
        "host": "",
        "port": 1080,
        "username": "me",             // (optional) Proxy username
        "password": "pass"            // (optional) Proxy password
    "smtp_port": 587                  // (optional) SMTP port to do the email verification, defaults to 25

2. Download the CLI [Full docs]

Note: The CLI binary doesn't connect to any backend, it checks the email directly from your computer.

Head to the releases page and download the binary for your platform.

> $ check_if_email_exists --help
check_if_email_exists 0.9.1
Check if an email address exists without sending an email.

    check_if_email_exists [FLAGS] [OPTIONS] [TO_EMAIL]

Check out the dedicated for all options and flags.

3. Programmatic Usage [Full docs]

In your own Rust project, you can add check-if-email-exists in your Cargo.toml:

check-if-email-exists = "0.9"

And use it in your code as follows:

use check_if_email_exists::{check_email, CheckEmailInput, CheckEmailInputProxy};

async fn check() {
    // Let's say we want to test the deliverability of
    let mut input = CheckEmailInput::new(vec!["".into()]);

    // Verify this email, using async/await syntax.
    let result = check_email(&input).await;

    // `result` is a `Vec<CheckEmailOutput>`, where the CheckEmailOutput
    // struct contains all information about our email.
    println!("{:?}", result);

The reference docs are hosted on

✈️ JSON Output

The output will be a JSON with the below format, the fields should be self-explanatory. For (note that it is disabled by Gmail), here's the exact output:

	"input": "",
	"is_reachable": "invalid",
	"misc": {
		"is_disposable": false,
		"is_role_account": false
	"mx": {
		"accepts_mail": true,
		"records": [
	"smtp": {
		"can_connect_smtp": true,
		"has_full_inbox": false,
		"is_catch_all": false,
		"is_deliverable": false,
		"is_disabled": true
	"syntax": {
		"domain": "",
		"is_valid_syntax": true,
		"username": "someone",
		"suggestion": null

What Does This Tool Check?

Included? Feature Description JSON field
Email reachability How confident are we in sending an email to this address? Can be one of safe, risky, invalid or unknown. is_reachable
Syntax validation Is the address syntactically valid? syntax.is_valid_syntax
DNS records validation Does the domain of the email address have valid MX DNS records? mx.accepts_mail
Disposable email address (DEA) validation Is the address provided by a known disposable email address provider? misc.is_disposable
SMTP server validation Can the mail exchanger of the email address domain be contacted successfully? smtp.can_connect_smtp
Email deliverability Is an email sent to this address deliverable? smtp.is_deliverable
Mailbox disabled Has this email address been disabled by the email provider? smtp.is_disabled
Full inbox Is the inbox of this mailbox full? smtp.has_full_inbox
Catch-all address Is this email address a catch-all address? smtp.is_catch_all
Role account validation Is the email address a well-known role account? misc.is_role_account
Gravatar Url The url of the Gravatar email address profile picture misc.gravatar_url
🔜 Free email provider check Is the email address bound to a known free email provider? Issue #89
🔜 Syntax validation, provider-specific According to the syntactic rules of the target mail provider, is the address syntactically valid? Issue #90
🔜 Honeypot detection Does email address under test hide a honeypot? Issue #91
🔜 Have I Been Pwned? Has this email been compromised in a data breach? Issue #289

🤔 Why?

Many online services (,, offer this service for a paid fee. Here is an open-source alternative to those tools.


check-if-email-exists's source code is provided under a dual license model.

Commercial license

If you want to use check-if-email-exists to develop commercial sites, tools, and applications, the Commercial License is the appropriate license. With this option, your source code is kept proprietary. Purchase a check-if-email-exists Commercial License at

Open source license

If you are creating an open-source application under a license compatible with the GNU Affero GPL license v3, you may use check-if-email-exists under the terms of the AGPL-3.0.

➡️ Read more about Reacher's license.


What does is_reachable: "unknown" mean?

This means that the server does not allow real-time verification of an email right now. It may happen for multiple reasons: your IP is blacklisted, the SMTP port 25 is blocked, the email account is momentarily receiving too many emails (spam protection)... or the email provider simply does not allow real-time verification at all. The details of this "unknown" case can be found in the smtp.error and mx.error fields.

The library hangs/takes a long time/doesn't show anything after 1 minute.

Most ISPs block outgoing SMTP requests through port 25, to prevent spam. check-if-email-exists needs to have this port open to make a connection to the email's SMTP server, so won't work behind these ISPs, and will instead hang until it times out. There's unfortunately no easy workaround for this problem, see for example this StackOverflow thread. One solution is to rent a Linux cloud server with a static IP and no blocked ports, see for example our Self-Host Guide for which cloud providers open port 25.

To see in detail what the binary is doing behind the scenes, run it in verbose mode with RUST_LOG=debug to see the logs.

I have another question.

Feel free to check out Reacher's FAQ.

🔨 Build From Source

Build the CLI from source or the HTTP backend from source.

Commit count: 1216

cargo fmt