net/smtp: No way to use other host name than "localhost" with helo command in smtp

[MBakhshi96]

net/smtp always uses localhost with helo command, and since localname in not exported in Client struct, you can't change it not to use localhost. Here you can find Client struct inside net/smtp/smtp.go :

// A Client represents a client connection to an SMTP server.
type Client struct {
	// Text is the textproto.Conn used by the Client. It is exported to allow for
	// clients to add extensions.
	Text *textproto.Conn
	// keep a reference to the connection so it can be used to create a TLS
	// connection later
	conn net.Conn
	// whether the Client is using TLS
	tls        bool
	serverName string
	// map of supported extensions
	ext map[string]string
	// supported auth mechanisms
	auth       []string
	localName  string // the name to use in HELO/EHLO
	didHello   bool   // whether we've said HELO/EHLO
	helloError error  // the error from the hello
}

This way it's not possible to start smtp with any other mail server not running on localhost.

[AlexRouSg]

https://golang.org/pkg/net/smtp/#Client.Hello

Hello sends a HELO or EHLO to the server as the given host name. Calling this method is only necessary if the client needs control over the host name used. The client will introduce itself as "localhost" automatically otherwise. If Hello is called, it must be called before any of the other methods.

func (c *Client) Hello(localName string) error {
        ...
	c.localName = localName
	return c.hello()
}