A SMTP Server Package 
a simple smtp server library, forked from This repo but I refactored it to be more advanced and organized
Features
- Very simple
- Automated SPF Checks
- Automated
FROMvalidation (MXchecking), viaRequest.Mailable - Supports TLS
- Modular, as you can add more smtp command processors to extend the functionality as you need
Quick Start
go get github.com/alash3al/go-smtpsrv
package main
import (
"fmt"
"github.com/alash3al/go-smtpsrv"
)
func main() {
handler := func(req *smtpsrv.Request) error {
// ...
return nil
}
srv := &smtpsrv.Server{
Name: "mail.my.server",
Addr: ":25025",
MaxBodySize: 5 * 1024,
Handler: handler,
}
fmt.Println(srv.ListenAndServe())
}
Security
The smtp server also supports the STARTTLS option, if you use the ListenAndServeTLS variant.
You can also further customize the tls config as well.
server := smtp.Server{Name: "example.com", Debug: true}
config := &tls.Config{MinVersion:tls.VersionSSL30}
server.TLSConfig = config
log.Fatal(server.ListenAndServeTLS(":smtp", "cert.pem", "key.pem", nil))
Authentication
The smtp server also supports authentication via the PLAIN method. Ideally this would be
coupled with STARTTLS to ensure secrecy of passwords in transit. You can do this by creating
a custom server and registering the AUTH callback. This will be called everytime someone
attempts to authenticate.
server.Auth = func(username, password, remoteAddress string) error {
if username == "user" && password == "p@$$w0rd" {
return nil
}
return errors.New("Nope!")
}
Addressing and preventing open-relay
Since your callback is only called once the smtp protocol has progressed to the data point,
meaning the sender and recipient have been specified, the server also offers an Addressable
callback that can be used to deny unknown recipients.
server.Addressable = func(user, address string) bool {
if user != ""{
//Allow relay for authenticated users
return true
}
if strings.HasSuffix(address, "example.com"){
return true
}
return false
}