golang net/smtp getting smtp server response DSN

Question

I am using golang net/smtp to send mails

Whenever I send to my smtp server I need to capture the response from the server Especially the DSN

For example my local smtp server gives a "ok queued as " at the end of the mail

I need to capture this and print in the logs

How can I do this

package main

import (
    "log"
    "net/smtp"
)

func sendEmail(msg []byte) {
    c, err := smtp.Dial("localhost:25")
    if err != nil {
        log.Fatal(err)
    }
    if err := c.Mail("[email protected]"); err != nil {
        log.Fatal(err)
    }

    if err := c.Rcpt("[email protected]"); err != nil {
        log.Fatal(err)
    }
    wc, err := c.Data()
    if err != nil {
        log.Fatal(err)
    }

    _, err = wc.Write(msg)
    if err != nil {
        log.Fatal(err)
    }

    //How do I get the response here ??
    err = wc.Close()
    if err != nil {
        log.Fatal(err)
    }

    err = c.Quit()
    if err != nil {
        log.Fatal(err)
    }
}

Answer 1

As mentioned in the comments you can use c.Text.ReadResponse():

package main

import (
    "net/smtp"
)

func sendEmail(msg []byte) (code int, message string, err error) {
    c, err := smtp.Dial("localhost:25")
    if err != nil {
        return
    }
    defer c.Quit() // make sure to quit the Client

    if err = c.Mail("[email protected]"); err != nil {
        return
    }

    if err = c.Rcpt("[email protected]"); err != nil {
        return
    }

    wc, err := c.Data()
    if err != nil {
        return
    }
    defer wc.Close() // make sure WriterCloser gets closed

    _, err = wc.Write(msg)
    if err != nil {
        return
    }

    code, message, err = c.Text.ReadResponse(0)
    return
}

---

The code, message and any err are now passed to the caller, don't use log.Fatal throughout your code, handle the error on the calling side.

Answer 2

package main

import (
    "net/smtp"
)

func sendEmail(msg []byte) (code int, message string, err error) {
    c, err := smtp.Dial("localhost:25")
    if err != nil {
        return
    }
    defer c.Quit() // make sure to quit the Client

    if err = c.Mail("[email protected]"); err != nil {
        return
    }

    if err = c.Rcpt("[email protected]"); err != nil {
        return
    }

    wc, err := c.Data()
    if err != nil {
        return
    }

    _, err = wc.Write(msg)
    if err != nil {
        return
    }

    code, message, err = closeData(c) 
    if err != nil {
        return 0, "", err
    }
    
    return code, message, err
}


func closeData(client *smtp.Client) error {
    d := &dataCloser{
        c:           client,
        WriteCloser: client.Text.DotWriter(),
    }

    return d.Close()
}

type dataCloser struct {
    c *smtp.Client
    io.WriteCloser
}

func (d *dataCloser) Close() (int, string, error) {
    d.WriteCloser.Close() // make sure WriterCloser gets closed
    code, message, err := d.c.Text.ReadResponse(250)

    fmt.Printf("Message %v, Error %v\n", message, err)
    return code, message, err
}