blackmail

README

Blackmail is a Go package to send emails.

Current status: work-in-progress. Most of it works, but the API isn't stable yet and some things are not yet implemented as documented.

Why a new package? I didn't care much for the API of many of the existing solutions.

Import the library as zgo.at/blackmail; API docs: https://godocs.io/zgo.at/blackmail

There is also a smtp client library at zgo.at/blackmail/smtp which can be used without the main blackmail client if you want. It's a modified version of net/smtp (via go-smtp, although I removed most added features from that).

There is a small commandline utility at cmd/blackmail; try it with go run ./cmd/blackmail.

The main use case where you just want to send off an email and be done with it. Non-goals include things like parsing email messages, support for encodings other than ASCII and UTF-8, or a one-stop-shop for your very specific complex requirements. It should be able to handle all common (and not-so-common) use cases though.

Example

// Send a new message using blackmail.DefaultMailer
err := blackmail.Send("Send me bitcoins or I will leak your browsing history!",
    blackmail.From("", "blackmail@example.com"),
    blackmail.To("Name", "victim@example.com"),
    blackmail.Bodyf("I can haz ur bitcoinz?"))

// A more complex message with a text and HTML part and inline image.
err = blackmail.Send("I saw what you did last night 😏",
    blackmail.From("😏", "blackmail@example.com"),
    append(blackmail.To("Name", "victim@example.com"), blackmail.Cc("Other", "other@example.com")...),
    blackmail.Text("Text part")
    blackmail.HTML("HTML part: <img src="cid:blackmail:1">",
        blackmail.InlineImage("image/png", "logo.png", imgbytes)))

// You can create your own (re-usable) mailer.
mailer := blackmail.NewMailer("smtp://user:pass@localhost:25")
err = mailer.Send([..])

// Add some options to your mailer.
mailer = blackmail.NewMailer("smtp://user:pass@localhost:25
    blackmail.MailerAuth(..),
    blackmail.MailerTLS(&tls.Config{}),
    blackmail.RequireSTARTLS(true))

// Get RF5322 message with a list of recipients to send it to (To + Cc + Bcc).
msg, to := blackmail.Message([.. same arguments as Send() ..])

See the test cases in blackmail_test.go for various other examples.

Questions you may have

I get the error "tls: first record does not look like a TLS handshake"

You are attempting to establish a TLS connection to a server which doesn't support TLS or only supports it via the STARTTLS command.

I get the error "x509: certificate signed by unknown authority"

The certificate chain used for the TLS connection is not signed by a known authority. It's a self-signed certificate or you don't have the root certificates installed.

How can I use a @ in my username?

Encode as %40:

smtp://carpetsmoker%40fastmail.nl:PASS@smtp.fastmail.com:587'

Dedication

I first had the idea of blackmail well over 10 years ago after seeing some Joe Armstrong interview where he mentioned he or a co-worker (I forgot) maintained an email client in the 80s blackmail. I rewrote my PHP "mailview" webmail client to Python years ago and called it blackmail, but never finished or released it.

Finally, after all these years I have a change to steal use the blackmail name for an email-related thing!

This package is dedicated to Joe Armstrong. I never programmed Erlang, but found many of his writings and talks insightful, and – more importantly – he was a funny guy.

…and now for the tricky bit…

Documentation

Overview

Package blackmail sends emails.

Index

• Constants
• Variables
• func Attachment(contentType, filename string, body []byte) bodyPart
• func Bcc(addr ...string) []recipient
• func BccAddress(addr ...mail.Address) []recipient
• func BccNames(nameAddr ...string) []recipient
• func Body(contentType string, body []byte) bodyPart
• func BodyHTML(body []byte, images ...bodyPart) bodyPart
• func BodyMust(contentType string, fn func() ([]byte, error)) bodyPart
• func BodyMustHTML(fn func() ([]byte, error)) bodyPart
• func BodyMustText(fn func() ([]byte, error)) bodyPart
• func BodyText(body []byte) bodyPart
• func Bodyf(s string, args ...interface{}) bodyPart
• func Cc(addr ...string) []recipient
• func CcAddress(addr ...mail.Address) []recipient
• func CcNames(nameAddr ...string) []recipient
• func From(name, address string) mail.Address
• func Headers(keyValue ...string) bodyPart
• func HeadersAutoreply() bodyPart
• func InlineImage(contentType, filename string, body []byte) bodyPart
• func MailerAuth(v string) senderOpt
• func MailerOut(v io.Writer) senderOpt
• func MailerRequireTLS(v bool) senderOpt
• func MailerTLS(v *tls.Config) senderOpt
• func Message(subject string, from mail.Address, rcpt []recipient, firstPart bodyPart, ...) ([]byte, []string, error)
• func NopCloser(r io.Writer) io.WriteCloser
• func Send(subject string, from mail.Address, rcpt []recipient, firstPart bodyPart, ...) error
• func To(addr ...string) []recipient
• func ToAddress(addr ...mail.Address) []recipient
• func ToNames(nameAddr ...string) []recipient
• type Mailer
  • func NewMailer(smtp string, opts ...senderOpt) Mailer
  • func (m Mailer) Send(subject string, from mail.Address, rcpt []recipient, firstPart bodyPart, ...) error
• type SoftError
  • func (f SoftError) Error() string
  • func (f SoftError) Unwrap() error

Constants

const (
	ConnectWriter = "writer" // Write to an io.Writer.
	ConnectDirect = "direct" // Connect directly to MX records.
)

const (
	AuthLogin   = "login"
	AuthPlain   = "plain"
	AuthCramMD5 = "cram-md5"
)

Authentication methods for MailerAuth().

Variables

var DefaultMailer = NewMailer(ConnectDirect)

DefaultMailer is used with blackmail.Send().

Functions

func Attachment

func Attachment(contentType, filename string, body []byte) bodyPart

Attachment returns a new attachment part with the given Content-Type.

It will try to guess the Content-Type if empty.

func Bcc

func Bcc(addr ...string) []recipient

func BccAddress

func BccAddress(addr ...mail.Address) []recipient

func BccNames

func BccNames(nameAddr ...string) []recipient

func Body

func Body(contentType string, body []byte) bodyPart

Body returns a new part with the given Content-Type.

func BodyHTML

func BodyHTML(body []byte, images ...bodyPart) bodyPart

BodyHTML returns a new text/html part.

func BodyMust

func BodyMust(contentType string, fn func() ([]byte, error)) bodyPart

BodyMust sets the body using a callback, propagating any errors back up.

This is useful when using Go templates for the mail body;

buf := new(bytes.Buffer)
err := tpl.ExecuteTemplate(buf, "email", struct{
    Name string
}{"Martin"})
if err != nil {
    log.Fatal(err)
}

err := Send("Basic test", From("", "me@example.com"),
    To("to@to.to"),
    Body("text/plain", buf.Bytes()))

With BodyMust(), it's simpler; you just need to define a little helper re-usable helper function and call that:

func template(tplname string, args interface{}) func() ([]byte, error) {
    return func() ([]byte, error) {
        buf := new(bytes.Buffer)
        err := tpl.ExecuteTemplate(buf, tplname, args)
        return buf.Bytes(), err
    }
}

err := Send("Basic test", From("", "me@example.com"),
    To("to@to.to"),
    BodyMust("text/html", template("email", struct {
        Name string
    }{"Martin"})))

Other use cases include things like loading data from a file, reading from a stream, etc.

func BodyMustHTML

func BodyMustHTML(fn func() ([]byte, error)) bodyPart

BodyMustHTML is like BodyMust() with contentType text/html.

func BodyMustText

func BodyMustText(fn func() ([]byte, error)) bodyPart

BodyMustText is like BodyMust() with contentType text/plain.

func BodyText

func BodyText(body []byte) bodyPart

BodyText returns a new text/plain part.

func Bodyf

func Bodyf(s string, args ...interface{}) bodyPart

Bodyf returns a new text/plain part.

func Cc

func Cc(addr ...string) []recipient

func CcAddress

func CcAddress(addr ...mail.Address) []recipient

func CcNames

func CcNames(nameAddr ...string) []recipient

func From

func From(name, address string) mail.Address

From makes creating a mail.Address a bit more convenient.

mail.Address{Name: "foo, Address: "foo@example.com}
blackmail.From{"foo, "foo@example.com)

func Headers

func Headers(keyValue ...string) bodyPart

Headers adds the headers to the message.

This will override any headers set automatically by the system, such as Date: or Message-Id:

Headers("My-Header", "value",
    "Message-Id", "<my-message-id@example.com>")

func HeadersAutoreply

func HeadersAutoreply() bodyPart

HeadersAutoreply sets headers to indicate this message is a an autoreply.

See e.g: https://www.arp242.net/autoreply.html#what-you-need-to-set-on-your-auto-response

func InlineImage

func InlineImage(contentType, filename string, body []byte) bodyPart

InlineImage returns a new inline image part.

It will try to guess the Content-Type if empty.

Then use "cid:blackmail:<n>" to reference it:

<img src="cid:blackmail:1">     First InlineImage()
<img src="cid:blackmail:2">     Second InlineImage()

func MailerAuth

func MailerAuth(v string) senderOpt

MailerAuth sets the AUTH method for the relay mailer. Currently LOGIN, PLAIN, and CRAM-MD5 are supported.

In general, PLAIN is preferred and it's the default. Note that CRAM-MD5 only provides weak security over untrusted connections.

func MailerOut

func MailerOut(v io.Writer) senderOpt

MailerOut sets the output for the writer mailer.

func MailerRequireTLS

func MailerRequireTLS(v bool) senderOpt

MailerRequireTLS sets whether TLS is required.

func MailerTLS

func MailerTLS(v *tls.Config) senderOpt

MailerTLS sets the tls config for the relay and direct mailer.

func Message

func Message(subject string, from mail.Address, rcpt []recipient, firstPart bodyPart, parts ...bodyPart) ([]byte, []string, error)

Message formats a message.

func NopCloser

func NopCloser(r io.Writer) io.WriteCloser

func Send

func Send(subject string, from mail.Address, rcpt []recipient, firstPart bodyPart, parts ...bodyPart) error

Send an email using the DefaultMailer.

The arguments are identical to Message().

func To

func To(addr ...string) []recipient

To sets the To: from a list of email addresses.

func ToAddress

func ToAddress(addr ...mail.Address) []recipient

ToAddress sets the To: from a list of mail.Addresses.

func ToNames

func ToNames(nameAddr ...string) []recipient

ToNames sets the To: from a list of "name", "addr" arguments.

Types

type Mailer

type Mailer struct {
	// contains filtered or unexported fields
}

Mailer to send messages; use NewMailer() to construct a new instance.

func NewMailer

func NewMailer(smtp string, opts ...senderOpt) Mailer

NewMailer returns a new re-usable mailer.

Setting the connection string to blackmail.Writer will print all messages to stdout without sending them:

NewMailer(blackmail.Writer)

You can pass Mailer.Writer() as an option to send them somewhere else:

NewMailer(blackmail.Writer, blackmail.MailerOut(os.Stderr))

buf := new(bytes.Buffer)
NewMailer(blackmail.Writer, blackmail.MailerOut(buf))

If the connection string is set to blackmail.Direct, blackmail will look up the MX records and attempt to deliver to them.

NewMailer(blackmail.Direct)

Any URL will be used as a SMTP relay:

NewMailer("smtps://foo:foo@mail.foo.com")

The default authentication is PLAIN; add MailerAuth() to set something different.

func (Mailer) Send

func (m Mailer) Send(subject string, from mail.Address, rcpt []recipient, firstPart bodyPart, parts ...bodyPart) error

Send an email.

The arguments are identical to Message().

type SoftError

type SoftError struct {
	// contains filtered or unexported fields
}

func (SoftError) Error

func (f SoftError) Error() string

func (SoftError) Unwrap

func (f SoftError) Unwrap() error