#email #smtp #verification #mx


Check if an email address exists without sending any email

11 releases (4 breaking)

✓ Uses Rust 2018 edition

new 0.8.5 May 21, 2020
0.8.4 May 13, 2020
0.7.1 Apr 14, 2020
0.6.1 Feb 18, 2020
0.4.0 Oct 21, 2019

#11 in Email

Download history 7/week @ 2020-01-25 6/week @ 2020-02-01 11/week @ 2020-02-08 49/week @ 2020-02-15 35/week @ 2020-02-22 4/week @ 2020-02-29 124/week @ 2020-03-07 7/week @ 2020-03-14 14/week @ 2020-03-21 9/week @ 2020-03-28 9/week @ 2020-04-04 99/week @ 2020-04-11 4/week @ 2020-04-18 10/week @ 2020-04-25 247/week @ 2020-05-02 127/week @ 2020-05-09

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Check if an email address exists before sending the email.

👉 Live Demo: https://reacher.email

You can also: Deploy

IMPORTANT: This software is licensed under the AGPL-3.0 license, which forbids it being integrated and distributed in closed-source commercials projects. Message me if you wish an alternate licensing.

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
🔜 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
🔜 Gravatar Does this email address have a Gravatar profile picture? Issue #92
🔜 Have I Been Pwned? Has this email been compromised in a data breach? Issue #289

🤔 Why?

Many online services (https://hunter.io, https://verify-email.org, https://email-checker.net) offer this service for a paid fee. Here is an open-source alternative to those tools.

Try It Yourself

There are 5 ways you can try check-if-email-exists.

1. Use the Hosted Version: https://reacher.email 🥇

This simple SaaS is also open-source by the way: https://github.com/reacherhq.

If you would like to self-host it yourself and have questions, send me a message.

2. Deploy to Heroku


Heroku's servers have SMTP port 25 open, and have static IPs able to connect to most email providers (unless of course if you start heavily spamming these providers).

3. Use Docker

The Docker image is hosted on Docker Hub: https://hub.docker.com/r/amaurymartiny/check-if-email-exists.

To run it, run the following command:

docker run -p 3000:3000 amaurymartiny/check-if-email-exists

You can then send a POST request with the following body to http://localhost:3000 to test multiple emails at once:

	"to_emails": ["someone@gmail.com"]

Here's the equivalent curl command:

curl -X POST -d'{"to_emails":["someone@gmail.com"]}' http://localhost:3000

Optionally, you can also pass in from_email and hello_name fields into the JSON object, see the help message below to understand their meanings.

4. Download the Binary

Note: The 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. Make sure you have openssl installed on your local machine.

> $ check_if_email_exists --help
check_if_email_exists 0.8.5
Check if an email address exists without sending any email.

    check_if_email_exists [FLAGS] [OPTIONS] [TO_EMAIL]

        --http       Runs a HTTP server.
    -h, --help       Prints help information
    -V, --version    Prints version information

        --from-email <FROM_EMAIL>    The email to use in the `MAIL FROM:` SMTP command. [default: user@example.org]
        --hello-name <HELLO_NAME>    The name to use in the `EHLO:` SMTP command. [default: localhost]
        --http-host <HOST>           Sets the host IP address on which the HTTP server should bind. Only used when
                                     `--http` flag is on. [default:]
        --http-port <PORT>           Sets the port on which the HTTP server should bind. Only used when `--http` flag is
                                     on. If not set, then it will use $PORT, or default to 3000.
        --proxy-host <PROXY_HOST>    Use the specified SOCKS5 proxy host to perform email verification.
        --proxy-port <PROXY_PORT>    Use the specified SOCKS5 proxy port to perform email verification. Only used when
                                     `--proxy-host` flag is set. [default: 1080]

    <TO_EMAIL>    The email to check.

If you run with the --http flag, check-if-email-exists will serve a HTTP server on http://localhost:3000. You can then send a POST request with the following body to test multiple emails at once:

	"to_emails": ["someone@gmail.com"]

Here's the equivalent curl command:

curl -X POST -d'{"to_emails":["someone@gmail.com"]}' http://localhost:3000

Optionally, you can also pass in from_email and hello_name fields into the JSON object, see the help message above to understand their meanings.

💡 PRO TIP: To show debug logs when running the binary, run:

RUST_LOG=debug check_if_email_exists [FLAGS] [OPTIONS] [TO_EMAIL]

5. Usage as a Rust Library

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

check-if-email-exists = "0.8"

And use it in your code as follows:

use check_if_email_exists::{check_email, CheckEmailInput};

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

    // Optionally, we can also tweak the configuration parameters used in the
    // verification.
        .from_email("me@example.org".into()) // Used in the `MAIL FROM:` command
        .hello_name("example.org".into()); // Used in the `EHLO` command

    // Verify this input, 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 docs.rs.

✈️ JSON Output

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

	"input": "someone@gmail.com",
	"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": "gmail.com",
		"is_valid_syntax": true,
		"username": "someone"

You can also take a look at the OpenAPIv3 specification of this JSON object.


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 Deploy to Heroku section.

To see in details what the binary is doing behind the scenes, run it in verbose mode to see the logs.

The output shows "connection refused" in the smtp.error field.

This also happens when your ISP block SMTP ports, see the above answer.

🔨 Build From Source

First, install Rust; you'll need Rust 1.37.0 or later. Then, run the following commands:

# Download the code
$ git clone https://github.com/amaurymartiny/check-if-email-exists
$ cd check-if-email-exists

# Build in release mode
$ cargo build --release

# Run the binary
$ ./target/release/check_if_email_exists --help

Legacy Bash Script

The 1st version of this tool was a simple bash script which made a telnet call. If you would like to use that simpler version, have a look at the legacy branch. The reasons for porting the bash script to the current codebase are explained in this issue.

📜 License

The source code is available under the license beard dude loves. See the LICENSE file for more info.

🌯 Falafel Wrap


I don't drink coffee, but I'd enjoy a wrap from my favorite Falafel dealer. 👉 See which one.


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