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# email-verifier # Contributions to AfterShip/email-verifier
✉️ A Go library for email verification without sending any emails. :white_check_mark: A Go library for email verification without sending any emails.
[![Build Status](https://github.com/AfterShip/email-verifier/workflows/CI%20Actions/badge.svg)](https://github.com/AfterShip/email-verifier/actions) This repository holds only my commits to the upstream project, with their original author, date and diff.
[![Godoc](http://img.shields.io/badge/godoc-reference-blue.svg?style=flat)](https://godoc.org/github.com/AfterShip/email-verifier) Each of my commits is preceded by a snapshot of the upstream files it touched, so every diff shows exactly what I changed.
[![Coverage Status](https://coveralls.io/repos/github/AfterShip/email-verifier/badge.svg?t=VTgVfL)](https://coveralls.io/github/AfterShip/email-verifier)
[![Go Report Card](https://goreportcard.com/badge/github.com/AfterShip/email-verifier)](https://goreportcard.com/report/github.com/AfterShip/email-verifier)
[![license](http://img.shields.io/badge/license-MIT-red.svg?style=flat)](https://github.com/AfterShip/email-verifier/blob/main/LICENSE)
## Features ## Merged pull requests
- Email Address Validation: validates if a string contains a valid email. - [Document the proxy schemes that work and stop panicking on custom dialers](https://github.com/AfterShip/email-verifier/pull/224) (2026-09-15)
- Email Verification Lookup via SMTP: performs an email verification on the passed email (catchAll detection enabled by default)
- MX Validation: checks the DNS MX records for the given domain name
- Misc Validation: including Free email provider check, Role account validation, Disposable emails address (DEA) validation
- Email Reachability: checks how confident in sending an email to the address
## Install
Use `go get` to install this package.
```shell script
go get -u github.com/AfterShip/email-verifier
```
### Supported Go versions
The three most recent Go releases, currently **1.25, 1.26 and 1.27**, each covered by CI.
`go.mod` requires the oldest of them, so an older toolchain will refuse to build this module.
## Usage
### Basic usage
Use `Verify` method to verify an email address with different dimensions
```go
package main
import (
"fmt"
emailverifier "github.com/AfterShip/email-verifier"
)
var (
verifier = emailverifier.NewVerifier()
)
func main() {
email := "example@exampledomain.org"
ret, err := verifier.Verify(email)
if err != nil {
fmt.Println("verify email address failed, error is: ", err)
return
}
if !ret.Syntax.Valid {
fmt.Println("email address syntax is invalid")
return
}
fmt.Println("email validation result", ret)
/*
result is:
{
"email":"example@exampledomain.org",
"disposable":false,
"reachable":"unknown",
"role_account":false,
"free":false,
"syntax":{
"username":"example",
"domain":"exampledomain.org",
"valid":true
},
"has_mx_records":true,
"smtp":null,
"gravatar":null
}
*/
}
```
### Email verification Lookup
Use `CheckSMTP` to performs an email verification lookup via SMTP.
```go
var (
verifier = emailverifier.
NewVerifier().
EnableSMTPCheck()
)
func main() {
domain := "domain.org"
username := "username"
ret, err := verifier.CheckSMTP(domain, username)
if err != nil {
fmt.Println("check smtp failed: ", err)
return
}
fmt.Println("smtp validation result: ", ret)
}
```
If you want to disable catchAll checking, use the `DisableCatchAllCheck()` switch (in effect only when SMTP verification is enabled).
```go
verifier = emailverifier.
NewVerifier().
EnableSMTPCheck().
DisableCatchAllCheck()
```
> Note: because most of the ISPs block outgoing SMTP requests through port 25 to prevent email spamming, the module will not perform SMTP checking by default. You can initialize the verifier with `EnableSMTPCheck()` to enable such capability if port 25 is usable,
> or use a socks proxy to connect over SMTP
> Note: set `FromEmail()` and `HelloName()` before verifying at any volume. The defaults are
> `user@example.org` and `localhost`, and `example.org` is reserved by RFC 2606, so a server
> that validates the sender can reject the whole exchange before it ever considers the
> address you asked about. Rejections of this kind arrive at `MAIL FROM` and name the sender
> or the connecting host rather than the recipient, for example
> `550 5.7.25 Forward-confirmed reverse DNS failed` or
> `550 5.7.1 Service unavailable, Client host [...] blocked using Spamhaus`. Use a domain you
> control, with a PTR record for the IP you connect from.
### Use a SOCKS5 proxy to verify email
Support setting a SOCKS5 proxy to verify the email, proxyURI should be in the format: `socks5://user:password@127.0.0.1:1080`
The scheme must be `socks5` or `socks5h`, the only two `golang.org/x/net/proxy` resolves.
Anything else, `socks4` and `socks4a` included, fails the dial with `proxy: unknown scheme`;
add it with [`proxy.RegisterDialerType`](https://pkg.go.dev/golang.org/x/net/proxy#RegisterDialerType)
before calling `Proxy()`.
```go
var (
verifier = emailverifier.
NewVerifier().
EnableSMTPCheck().
Proxy("socks5://user:password@127.0.0.1:1080")
)
func main() {
domain := "domain.org"
username := "username"
ret, err := verifier.CheckSMTP(domain, username)
if err != nil {
fmt.Println("check smtp failed: ", err)
return
}
fmt.Println("smtp validation result: ", ret)
}
```
Two things to know about the proxy:
> **A query string in the proxy URI is ignored.** `golang.org/x/net/proxy` reads only the
> scheme, credentials and host, so a `?timeout=5s` has no effect. Use `ConnectTimeout()` and
> `OperationTimeout()` instead.
> **DNS does not go through the proxy.** Only the connection to the mail server does, so MX
> lookups still leave from the local machine. To route them through the proxy as well, dial
> your DNS server over TCP through it — SOCKS5 carries TCP, and Go frames DNS over a
> non-packet connection per RFC 7766:
>
> ```go
> socksDialer, err := proxy.SOCKS5("tcp", "127.0.0.1:1080", nil, proxy.Direct)
> if err != nil {
> return err
> }
> verifier = emailverifier.
> NewVerifier().
> EnableSMTPCheck().
> Proxy("socks5://127.0.0.1:1080").
> Resolver(&net.Resolver{
> PreferGo: true,
> Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
> // ignore network, which may be "udp": SOCKS5 CONNECT carries TCP only
> return socksDialer.Dial("tcp", "8.8.8.8:53")
> },
> })
> ```
>
> Each lookup opens a TCP connection through the proxy, so this costs more than plain UDP DNS.
### Use a custom DNS resolver
By default, the verifier uses `net.DefaultResolver` (the platform's system-configured DNS resolver) for MX lookups and direct SMTP host lookups. You can override this behaviour by supplying your own `*net.Resolver` via `Resolver()`, for example to query a specific DNS server. When a proxy is configured, SMTP hostname resolution follows the proxy path rather than this resolver. MX record lookups always use this resolver, whether or not a proxy is set.
```go
var (
verifier = emailverifier.
NewVerifier().
EnableSMTPCheck().
Resolver(&net.Resolver{
PreferGo: true,
Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
d := net.Dialer{}
return d.DialContext(ctx, network, "8.8.8.8:53")
},
})
)
func main() {
domain := "domain.org"
username := "username"
ret, err := verifier.CheckSMTP(domain, username)
if err != nil {
fmt.Println("check smtp failed: ", err)
return
}
fmt.Println("smtp validation result: ", ret)
}
```
> Note: `PreferGo: true` is doing real work here, it is not boilerplate. MX record lookups always
> go through Go's own DNS client, so a custom `Dial` is honoured for those either way. Resolving
> the mail server's hostname to an IP for the TCP connection is different: without `PreferGo` that
> step may use the system (cgo) resolver, which ignores `Dial` entirely and quietly falls back to
> `/etc/resolv.conf`. Even with it set, `/etc/hosts` is still consulted before DNS, so a host
> listed there never reaches your resolver.
### Misc Validation
To check if an email domain is disposable via `IsDisposable`
```go
var (
verifier = emailverifier.
NewVerifier().
EnableAutoUpdateDisposable()
)
func main() {
domain := "domain.org"
if verifier.IsDisposable(domain) {
fmt.Printf("%s is a disposable domain\n", domain)
return
}
fmt.Printf("%s is not a disposable domain\n", domain)
}
```
> Note: It is possible to automatically update the disposable domains daily by initializing verifier with `EnableAutoUpdateDisposable()`
### Suggestions for domain typo
Will check for typos in an email domain in addition to evaluating its validity.
If we detect a possible typo, you will find a non-empty "suggestion" field in the validation result containing what we believe to be the correct domain.
Also, you can use the `SuggestDomain()` method alone to check the domain for possible misspellings
```go
func main() {
domain := "gmai.com"
suggestion := verifier.SuggestDomain(domain)
// suggestion should be `gmail.com`
if suggestion != "" {
fmt.Printf("domain %s is misspelled, right domain is %s. \n", domain, suggestion)
return
}
fmt.Printf("domain %s has no possible misspellings. \n", domain)
}
```
> Note: When using the `Verify()` method, domain typo checking is not enabled by default, you can enable it in a verifier with `EnableDomainSuggest()`
For more detailed documentation, please check on godoc.org 👉 [email-verifier](https://godoc.org/github.com/AfterShip/email-verifier)
## API
We provide a simple **self-hosted** [API server](https://github.com/AfterShip/email-verifier/tree/main/cmd/apiserver) script for reference.
The API interface is very simple. All you need to do is to send a GET request with the following URL.
The `email` parameter would be the target email you want to verify.
`https://{your_host}/v1/{email}/verification`
## Similar Libraries Comparison
| | [email-verifier](https://github.com/AfterShip/email-verifier) | [trumail](https://github.com/trumail/trumail) | [check-if-email-exists](https://reacher.email/) | [freemail](https://github.com/willwhite/freemail) |
| ----------------------------------- | :----------------------------------------------------------: | :-------------------------------------------: | :---------------------------------------------: | :-----------------------------------------------: |
| **Features** | 〰️ | 〰️ | 〰️ | 〰️ |
| Disposable email address validation | ✅ | ✅, but not available in free lib | ✅ | ✅ |
| Disposable address autoupdate | ✅ | 🤔 | ❌ | ❌ |
| Free email provider check | ✅ | ✅, but not available in free lib | ❌ | ✅ |
| Role account validation | ✅ | ❌ | ✅ | ❌ |
| Syntax validation | ✅ | ✅ | ✅ | ❌ |
| Email reachability | ✅ | ✅ | ✅ | ❌ |
| DNS records validation | ✅ | ✅ | ✅ | ❌ |
| Email deliverability | ✅ | ✅ | ✅ | ❌ |
| Mailbox disabled | ✅ | ✅ | ✅ | ❌ |
| Full inbox | ✅ | ✅ | ✅ | ❌ |
| Host exists | ✅ | ✅ | ✅ | ❌ |
| Catch-all | ✅ | ✅ | ✅ | ❌ |
| Gravatar | ✅ | ✅, but not available in free lib | ❌ | ❌ |
| Typo check | ✅ | ✅, but not available in free lib | ❌ | ❌ |
| Use proxy to connect over SMTP | ✅ | ❌ | ✅ | ❌ |
| Honeyport dection | 🔜 | ❌ | ❌ | ❌ |
| Bounce email check | 🔜 | ❌ | ❌ | ❌ |
| **Tech** | 〰️ | 〰️ | 〰️ | 〰️ |
| Provide API | ✅ | ✅ | ✅ | ❌ |
| Free API | ✅ | ❌ | ❌ | ❌ |
| Language | Go | Go | Rust | JavaScript |
| Active maintain | ✅ | ❌ | ✅ | ✅ |
| High Performance | ✅ | ❌ | ✅ | ✅ |
## FAQ
#### The library hangs/takes a long time after 30 seconds when performing email verification lookup via SMTP
Most ISPs block outgoing SMTP requests through port 25 to prevent email spamming. `email-verifier` needs to have this port open to make a connection to the email's SMTP server. With the port being blocked, it is not possible to perform such checking, and it will instead hang until timeout error. Unfortunately, there is no easy workaround for this issue.
For more information, you may also visit [this StackOverflow thread](https://stackoverflow.com/questions/18139102/how-to-get-around-an-isp-block-on-port-25-for-smtp).
#### The output shows `"connection refused"` in the `smtp.error` field.
This error can also be due to SMTP ports being blocked by the ISP, see the above answer.
#### What does reachable: "unknown" means
This means that the server does not allow real-time verification of an email right now, or the email provider is a catch-all email server.
## Credits
- [trumail](https://github.com/trumail/trumail)
- [check-if-email-exists](https://github.com/amaurymartiny/check-if-email-exists)
- [mailcheck](https://github.com/mailcheck/mailcheck)
- disposable domains from [disposable/disposable-email-domains](https://github.com/disposable/disposable-email-domains), both for the generated list and for `EnableAutoUpdateDisposable()`, less the few real providers it misclassifies (see `cmd/build_metadata/disposable_allowlist.txt`)
- free provider data from [HubSpot's free email domain list](https://f.hubspotusercontent40.net/hubfs/2832391/Marketing/Lead-Capture/free-domains-2.csv) and [tbrianjones/free_email_provider_domains](https://gist.github.com/tbrianjones/5992856), plus carrier and portal mailboxes vendored from [Kikobeats/free-email-domains](https://github.com/Kikobeats/free-email-domains)
## Contributing
For details on contributing to this repository, see the [contributing guide](https://github.com/AfterShip/email-verifier/blob/main/CONTRIBUTING.md).
## License
This package is licensed under MIT license. See [LICENSE](https://github.com/AfterShip/email-verifier/blob/main/LICENSE) for details.