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email sending library

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The library is a wrapper around the stdlib net/smtp simplifying email sending. It supports authentication, SSL/TLS, user-specified SMTP servers, content-type, charset, multiple recipients and more.

Usage example:

client := email.NewSender("localhost", email.ContentType("text/html"), email.Auth("user", "pass"))
err := client.Send("<html>some content, foo bar</html>",
    email.Params{From: "", To: []string{""}, Subject: "Hello world!",
        Attachments: []string{"/path/to/file1.txt", "/path/to/file2.txt"},
        InlineImages: []string{"/path/to/image1.png", "/path/to/image2.png"},


NewSender accepts a number of options to configure the client:

  • Port: SMTP port (default: 25)
  • TLS: Use TLS SMTP (default: false)
  • STARTTLS: Use STARTTLS (default: false)
  • Auth(user, password): Username and password for SMTP authentication (default: empty, no authentication)
  • LoginAuth: Use LOGIN mechanism instead of PLAIN mechanism for SMTP authentication, e.g. this is relevant for Office 365 and
  • ContentType: Content type for the email (default: “text/plain”)
  • Charset: Charset for the email (default: “utf-8”)
  • TimeOut: Timeout for the SMTP connection (default: 30 seconds)
  • Log: Logger to use (default: no logging)
  • SMTP: Set custom smtp client (default: none)

See go docs for Option functions.

Options should be passed to NewSender after the mandatory first (host) parameter.

sending email

To send email user need to create a sender first and then use Send method. The method accepts two parameters:

  • email content (string)
  • parameters (email.Params)
    type Params struct {
        From            string   // From email field
        To              []string // From email field
        Subject         string   // Email subject
        UnsubscribeLink string   // POST, -> "Use one-click unsubscribe"
        InReplyTo       string   // Identifier for email group (category), used for email grouping
        Attachments     []string // Attachments path
        InlineImages    []string // Embedding directly to email body. Autogenerated Content-Id (cid) equals to file name

See go docs for Send function.

technical details

  • Content-Transfer-Encoding set to quoted-printable
  • Custom SMTP client (smtp.Client from stdlib) can be set by user with SMTP option. In this case it will be used instead of making a new smtp client internally.
  • Logger can be set with Log option. It should implement email.Logger interface with a single Logf(format string, args ...interface{}) method. By default, “no logging” internal logger is used. This interface is compatible with the go-pkgz/lgr logger.
  • The library has no external dependencies, except for testing. It uses the stdlib net/smtp package.
  • SSL/TLS supported with TLS option (usually on port 465) as well as with STARTTLS (usually on port 587).


This library is not intended to be used for sending a lot of massive emails with low latency requirements. The intended use case is sending simple messages, like alerts, notification and so on. For example, sending alerts from a monitoring system, or for authentication-related emails, i.e. “password reset email”, “verification email”, etc.