#email #smtp #verification #mx


Check if an email address exists without sending any email

3 releases (breaking)

✓ Uses Rust 2018 edition

0.6.0 Dec 2, 2019
0.5.0 Nov 16, 2019
0.4.0 Oct 21, 2019

#28 in Email

24 downloads per month

GPL-3.0 license

453 lines


Check if an email address exists before sending the email.

Crate License

👉 Try it here: https://3nbyey1wsi.execute-api.us-east-1.amazonaws.com/dev/?to_email=YOUR_EMAIL_HERE

And replace the YOUR_EMAIL_HERE placeholder with the email you would like to verify.

Note: The above operation might take up to 1 minute.


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

Download the binary

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

Note: The binary doesn't connect to the above now.sh backend, it checks the mail directly from your computer.

CLI Usage

Make sure you have openssl installed.

    check_if_email_exists [OPTIONS] <TO_EMAIL>

    -h, --help       Prints help information
    -V, --version    Prints version information

        --from <FROM_EMAIL>    The from email to use in the SMTP connection [default: user@example.org]

    <TO_EMAIL>    The email to check

The output will be a JSON with the following format, for someone@gmail.com (note that it is disabled by Gmail):

	"mx": {
		"is_disposable": false,
		"records": [
	"smtp": {
		"has_full_inbox": false,
		"is_catch_all": false,
		"is_deliverable": false,
		"is_disabled": true
	"syntax": {
		"address": "someone@gmail.com",
		"domain": "gmail.com",
		"username": "someone",
		"valid_format": true

Verbose Mode

To show debug logs when running the binary, run:

RUST_LOG=debug check_if_email_exists [OPTIONS] <TO_EMAIL>

Usage as a Library

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

check-if-email-exists = "0.4"

And use it in your code as follows:

use check_if_email_exists::email_exists;

// First arg is the email we want to check, second arg is the FROM email used in the SMTP connection
let checked = email_exists("check.this.email@gmail.com", "user@example.org");

println!({:?}, checked); // `checked` is a SingleEmail struct


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

Most ISPs block outgoing SMTP requests through ports 25, 587 and 465, to prevent spam. check-if-email-exists needs to have these ports 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.

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

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.

Build From Source

First, install Rust; you'll need Rust 1.37.0 or later. Then, clone the source code locally:

# 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


GPL-3.0. See the LICENSE file for more info.


~198K SLoC