Merge pull request #57 from glaszig/starttls

allow disabling starttls

DOCS.md

@@ -10,6 +10,7 @@ You can configure the plugin using the following parameters:
 * **username** - SMTP username
 * **password** - SMTP password
 * **skip_verify** - Skip verification of SSL certificates, defaults to `false`
+* **starttls** - Enable/Disable STARTTLS
 * **recipients** - List of recipients to send this mail to (besides the commit author)
 * **recipients_file** - Filename to load additional recipients from (textfile with one email per line) (besides the commit author)
 * **recipients_only** - Do not send mails to the commit author, but only to **recipients**, defaults to `false`
@@ -127,3 +128,22 @@ steps:
       password: 12345
 +     skip_verify: true
 ```
+
+### STARTTLS
+
+By default, STARTTLS is being used opportunistically meaning, if advertised
+by the server, traffic is going to be encrypted.
+
+You may want to disable STARTTLS, e.g., with faulty and/or internal servers:
+
+```diff
+steps:
+  - name: notify
+    image: drillster/drone-email
+    settings:
+      from: noreply@github.com
+      host: smtp.mailgun.org
+      username: octocat
+      password: 12345
++     starttls: false
+```

main.go

@@ -66,6 +66,11 @@ func main() {
 			Usage:  "skip tls verify",
 			EnvVar: "PLUGIN_SKIP_VERIFY",
 		},
+		cli.BoolFlag{
+			Name:   "starttls",
+			Usage:  "Enable/Disable STARTTLS",
+			EnvVar: "PLUGIN_STARTTLS",
+		},
 		cli.StringFlag{
 			Name:   "recipients.file",
 			Usage:  "file to read recipients from",
@@ -407,6 +412,7 @@ func run(c *cli.Context) error {
 			Username:       c.String("username"),
 			Password:       c.String("password"),
 			SkipVerify:     c.Bool("skip.verify"),
+			StartTLS:       c.Bool("starttls"),
 			Recipients:     c.StringSlice("recipients"),
 			RecipientsFile: c.String("recipients.file"),
 			RecipientsOnly: c.Bool("recipients.only"),

plugin.go

@@ -9,7 +9,7 @@ import (
 	"github.com/aymerick/douceur/inliner"
 	"github.com/drone/drone-go/template"
 	"github.com/jaytaylor/html2text"
-	"gopkg.in/gomail.v2"
+	gomail "gopkg.in/mail.v2"
 )
 
 type (
@@ -88,6 +88,7 @@ type (
 		Username       string
 		Password       string
 		SkipVerify     bool
+		StartTLS       bool
 		Recipients     []string
 		RecipientsFile string
 		RecipientsOnly bool
@@ -147,9 +148,15 @@ func (p Plugin) Exec() error {
 	} else {
 		dialer = gomail.NewDialer(p.Config.Host, p.Config.Port, p.Config.Username, p.Config.Password)
 	}
+
 	if p.Config.SkipVerify {
 		dialer.TLSConfig = &tls.Config{InsecureSkipVerify: true}
 	}
+
+	if !p.Config.StartTLS {
+		dialer.StartTLSPolicy = gomail.NoStartTLS
+	}
+
 	dialer.LocalName = p.Config.ClientHostname
 
 	closer, err := dialer.Dial()

vendor/gopkg.in/gomail.v2/CHANGELOG.md

@@ -1,20 +0,0 @@
-# Change Log
-All notable changes to this project will be documented in this file.
-This project adheres to [Semantic Versioning](http://semver.org/).
-
-## [2.0.0] - 2015-09-02
-
-- Mailer has been removed. It has been replaced by Dialer and Sender.
-- `File` type and the `CreateFile` and `OpenFile` functions have been removed.
-- `Message.Attach` and `Message.Embed` have a new signature.
-- `Message.GetBodyWriter` has been removed. Use `Message.AddAlternativeWriter`
-instead.
-- `Message.Export` has been removed. `Message.WriteTo` can be used instead.
-- `Message.DelHeader` has been removed.
-- The `Bcc` header field is no longer sent. It is far more simpler and
-efficient: the same message is sent to all recipients instead of sending a
-different email to each Bcc address.
-- LoginAuth has been removed. `NewPlainDialer` now implements the LOGIN
-authentication mechanism when needed.
-- Go 1.2 is now required instead of Go 1.3. No external dependency are used when
-using Go 1.5.

vendor/gopkg.in/gomail.v2/README.md

@@ -1,92 +0,0 @@
-# Gomail
-[![Build Status](https://travis-ci.org/go-gomail/gomail.svg?branch=v2)](https://travis-ci.org/go-gomail/gomail) [![Code Coverage](http://gocover.io/_badge/gopkg.in/gomail.v2)](http://gocover.io/gopkg.in/gomail.v2) [![Documentation](https://godoc.org/gopkg.in/gomail.v2?status.svg)](https://godoc.org/gopkg.in/gomail.v2)
-
-## Introduction
-
-Gomail is a simple and efficient package to send emails. It is well tested and
-documented.
-
-Gomail can only send emails using an SMTP server. But the API is flexible and it
-is easy to implement other methods for sending emails using a local Postfix, an
-API, etc.
-
-It is versioned using [gopkg.in](https://gopkg.in) so I promise
-there will never be backward incompatible changes within each version.
-
-It requires Go 1.2 or newer. With Go 1.5, no external dependencies are used.
-
-
-## Features
-
-Gomail supports:
-- Attachments
-- Embedded images
-- HTML and text templates
-- Automatic encoding of special characters
-- SSL and TLS
-- Sending multiple emails with the same SMTP connection
-
-
-## Documentation
-
-https://godoc.org/gopkg.in/gomail.v2
-
-
-## Download
-
-    go get gopkg.in/gomail.v2
-
-
-## Examples
-
-See the [examples in the documentation](https://godoc.org/gopkg.in/gomail.v2#example-package).
-
-
-## FAQ
-
-### x509: certificate signed by unknown authority
-
-If you get this error it means the certificate used by the SMTP server is not
-considered valid by the client running Gomail. As a quick workaround you can
-bypass the verification of the server's certificate chain and host name by using
-`SetTLSConfig`:
-
-    package main
-
-    import (
-    	"crypto/tls"
-
-    	"gopkg.in/gomail.v2"
-    )
-
-    func main() {
-    	d := gomail.NewDialer("smtp.example.com", 587, "user", "123456")
-    	d.TLSConfig = &tls.Config{InsecureSkipVerify: true}
-
-        // Send emails using d.
-    }
-
-Note, however, that this is insecure and should not be used in production.
-
-
-## Contribute
-
-Contributions are more than welcome! See [CONTRIBUTING.md](CONTRIBUTING.md) for
-more info.
-
-
-## Change log
-
-See [CHANGELOG.md](CHANGELOG.md).
-
-
-## License
-
-[MIT](LICENSE)
-
-
-## Contact
-
-You can ask questions on the [Gomail
-thread](https://groups.google.com/d/topic/golang-nuts/jMxZHzvvEVg/discussion)
-in the Go mailing-list.

vendor/gopkg.in/mail.v2/CHANGELOG.md

@@ -0,0 +1,88 @@
+# Change Log
+All notable changes to this project will be documented in this file.
+This project adheres to [Semantic Versioning](http://semver.org/).
+
+## *Unreleased*
+
+## [2.3.1] - 2018-11-12
+
+### Fixed
+
+- #39: Reverts addition of Go modules `go.mod` manifest.
+
+## [2.3.0] - 2018-11-10
+
+### Added
+
+- #12: Adds `SendError` to provide additional info about the cause and index of
+  a failed attempt to transmit a batch of messages.
+- go-gomail#78: Adds new `Message` methods for attaching and embedding
+  `io.Reader`s: `AttachReader` and `EmbedReader`.
+
+### Fixed
+
+- #26: Fixes RFC 1341 compliance by properly capitalizing the
+  `MIME-Version` header.
+- #30: Fixes IO errors being silently dropped in `Message.WriteTo`.
+
+## [2.2.0] - 2018-03-01
+
+### Added
+
+- #20: Adds `Message.SetBoundary` to allow specifying a custom MIME boundary.
+- #22: Adds `Message.SetBodyWriter` to make it easy to use text/template and
+  html/template for message bodies. Contributed by Quantcast.
+- #25: Adds `Dialer.StartTLSPolicy` so that `MandatoryStartTLS` can be required,
+  or `NoStartTLS` can disable it. Contributed by Quantcast.
+
+## [2.1.0] - 2017-12-14
+
+### Added
+
+- go-gomail#40: Adds `Dialer.LocalName` field to allow specifying the hostname
+  sent with SMTP's HELO command.
+- go-gomail#47: `Message.SetBody`, `Message.AddAlternative`, and
+  `Message.AddAlternativeWriter` allow specifying the encoding of message parts.
+- `Dialer.Dial`'s returned `SendCloser` automatically redials after a timeout.
+- go-gomail#55, go-gomail#56: Adds `Rename` to allow specifying filename
+  of an attachment.
+- go-gomail#100: Exports `NetDialTimeout` to allow setting a custom dialer.
+- go-gomail#70: Adds `Dialer.Timeout` field to allow specifying a timeout for
+  dials, reads, and writes.
+
+### Changed
+
+- go-gomail#52: `Dialer.Dial` automatically uses CRAM-MD5 when available.
+- `Dialer.Dial` specifies a default timeout of 10 seconds.
+- Gomail is forked from <https://github.com/go-gomail/gomail/> to
+  <https://github.com/go-mail/mail/>.
+
+### Deprecated
+
+- go-gomail#52: `NewPlainDialer` is deprecated in favor of `NewDialer`.
+
+### Fixed
+
+- go-gomail#41, go-gomail#42: Fixes a panic when a `Message` contains a
+  nil header.
+- go-gomail#44: Fixes `AddAlternativeWriter` replacing the message body instead
+  of adding a body part.
+- go-gomail#53: Folds long header lines for RFC 2047 compliance.
+- go-gomail#54: Fixes `Message.FormatAddress` when name is blank.
+
+## [2.0.0] - 2015-09-02
+
+- Mailer has been removed. It has been replaced by Dialer and Sender.
+- `File` type and the `CreateFile` and `OpenFile` functions have been removed.
+- `Message.Attach` and `Message.Embed` have a new signature.
+- `Message.GetBodyWriter` has been removed. Use `Message.AddAlternativeWriter`
+instead.
+- `Message.Export` has been removed. `Message.WriteTo` can be used instead.
+- `Message.DelHeader` has been removed.
+- The `Bcc` header field is no longer sent. It is far more simpler and
+efficient: the same message is sent to all recipients instead of sending a
+different email to each Bcc address.
+- LoginAuth has been removed. `NewPlainDialer` now implements the LOGIN
+authentication mechanism when needed.
+- Go 1.2 is now required instead of Go 1.3. No external dependency are used when
+using Go 1.5.

vendor/gopkg.in/mail.v2/README.md

@@ -0,0 +1,129 @@
+# Gomail
+[![Build Status](https://travis-ci.org/go-mail/mail.svg?branch=master)](https://travis-ci.org/go-mail/mail) [![Code Coverage](http://gocover.io/_badge/github.com/go-mail/mail)](http://gocover.io/github.com/go-mail/mail) [![Documentation](https://godoc.org/github.com/go-mail/mail?status.svg)](https://godoc.org/github.com/go-mail/mail)
+
+This is an actively maintained fork of [Gomail][1] and includes fixes and
+improvements for a number of outstanding issues. The current progress is
+as follows:
+
+ - [x] Timeouts and retries can be specified outside of the 10 second default.
+ - [x] Proxying is supported through specifying a custom [NetDialTimeout][2].
+ - [ ] Filenames are properly encoded for non-ASCII characters.
+ - [ ] Email addresses are properly encoded for non-ASCII characters.
+ - [ ] Embedded files and attachments are tested for their existence.
+ - [ ] An `io.Reader` can be supplied when embedding and attaching files.
+
+See [Transitioning Existing Codebases][3] for more information on switching.
+
+[1]: https://github.com/go-gomail/gomail
+[2]: https://godoc.org/gopkg.in/mail.v2#NetDialTimeout
+[3]: #transitioning-existing-codebases
+
+## Introduction
+
+Gomail is a simple and efficient package to send emails. It is well tested and
+documented.
+
+Gomail can only send emails using an SMTP server. But the API is flexible and it
+is easy to implement other methods for sending emails using a local Postfix, an
+API, etc.
+
+It requires Go 1.2 or newer. With Go 1.5, no external dependencies are used.
+
+
+## Features
+
+Gomail supports:
+- Attachments
+- Embedded images
+- HTML and text templates
+- Automatic encoding of special characters
+- SSL and TLS
+- Sending multiple emails with the same SMTP connection
+
+
+## Documentation
+
+https://godoc.org/github.com/go-mail/mail
+
+
+## Download
+
+If you're already using a dependency manager, like [dep][dep], use the following
+import path:
+
+```
+github.com/go-mail/mail
+```
+
+If you *aren't* using vendoring, `go get` the [Gopkg.in](http://gopkg.in)
+import path:
+
+```
+gopkg.in/mail.v2
+```
+
+[dep]: https://github.com/golang/dep#readme
+
+## Examples
+
+See the [examples in the documentation](https://godoc.org/github.com/go-mail/mail#example-package).
+
+
+## FAQ
+
+### x509: certificate signed by unknown authority
+
+If you get this error it means the certificate used by the SMTP server is not
+considered valid by the client running Gomail. As a quick workaround you can
+bypass the verification of the server's certificate chain and host name by using
+`SetTLSConfig`:
+
+```go
+package main
+
+import (
+	"crypto/tls"
+
+	"gopkg.in/mail.v2"
+)
+
+func main() {
+	d := mail.NewDialer("smtp.example.com", 587, "user", "123456")
+	d.TLSConfig = &tls.Config{InsecureSkipVerify: true}
+
+	// Send emails using d.
+}
+```
+
+Note, however, that this is insecure and should not be used in production.
+
+### Transitioning Existing Codebases
+
+If you're already using the original Gomail, switching is as easy as updating
+the import line to:
+
+```
+import gomail "gopkg.in/mail.v2"
+```
+
+## Contribute
+
+Contributions are more than welcome! See [CONTRIBUTING.md](CONTRIBUTING.md) for
+more info.
+
+
+## Change log
+
+See [CHANGELOG.md](CHANGELOG.md).
+
+
+## License
+
+[MIT](LICENSE)
+
+
+## Support & Contact
+
+You can ask questions on the [Gomail
+thread](https://groups.google.com/d/topic/golang-nuts/jMxZHzvvEVg/discussion)
+in the Go mailing-list.

vendor/gopkg.in/mail.v2/auth.go

@@ -1,4 +1,4 @@
-package gomail
+package mail
 
 import (
 	"bytes"

vendor/gopkg.in/mail.v2/doc.go

@@ -1,5 +1,6 @@
 // Package gomail provides a simple interface to compose emails and to mail them
 // efficiently.
 //
-// More info on Github: https://github.com/go-gomail/gomail
-package gomail
+// More info on Github: https://github.com/go-mail/mail
+//
+package mail

vendor/gopkg.in/mail.v2/errors.go

@@ -0,0 +1,16 @@
+package mail
+
+import "fmt"
+
+// A SendError represents the failure to transmit a Message, detailing the cause
+// of the failure and index of the Message within a batch.
+type SendError struct {
+	// Index specifies the index of the Message within a batch.
+	Index uint
+	Cause error
+}
+
+func (err *SendError) Error() string {
+	return fmt.Sprintf("gomail: could not send email %d: %v",
+		err.Index+1, err.Cause)
+}

vendor/gopkg.in/mail.v2/message.go

@@ -1,4 +1,4 @@
-package gomail
+package mail
 
 import (
 	"bytes"
@@ -18,6 +18,7 @@ type Message struct {
 	encoding    Encoding
 	hEncoder    mimeEncoder
 	buf         bytes.Buffer
+	boundary    string
 }
 
 type header map[string][]string
@@ -97,6 +98,11 @@ const (
 	Unencoded Encoding = "8bit"
 )
 
+// SetBoundary sets a custom multipart boundary.
+func (m *Message) SetBoundary(boundary string) {
+	m.boundary = boundary
+}
+
 // SetHeader sets a value to the given header field.
 func (m *Message) SetHeader(field string, value ...string) {
 	m.encodeHeader(value)
@@ -183,9 +189,15 @@ func (m *Message) GetHeader(field string) []string {
 }
 
 // SetBody sets the body of the message. It replaces any content previously set
-// by SetBody, AddAlternative or AddAlternativeWriter.
+// by SetBody, SetBodyWriter, AddAlternative or AddAlternativeWriter.
 func (m *Message) SetBody(contentType, body string, settings ...PartSetting) {
-	m.parts = []*part{m.newPart(contentType, newCopier(body), settings)}
+	m.SetBodyWriter(contentType, newCopier(body), settings...)
+}
+
+// SetBodyWriter sets the body of the message. It can be useful with the
+// text/template or html/template packages.
+func (m *Message) SetBodyWriter(contentType string, f func(io.Writer) error, settings ...PartSetting) {
+	m.parts = []*part{m.newPart(contentType, f, settings)}
 }
 
 // AddAlternative adds an alternative part to the message.
@@ -226,8 +238,8 @@ func (m *Message) newPart(contentType string, f func(io.Writer) error, settings
 }
 
 // A PartSetting can be used as an argument in Message.SetBody,
-// Message.AddAlternative or Message.AddAlternativeWriter to configure the part
-// added to a message.
+// Message.SetBodyWriter, Message.AddAlternative or Message.AddAlternativeWriter
+// to configure the part added to a message.
 type PartSetting func(*part)
 
 // SetPartEncoding sets the encoding of the part added to the message. By
@@ -283,8 +295,28 @@ func SetCopyFunc(f func(io.Writer) error) FileSetting {
 	}
 }
 
-func (m *Message) appendFile(list []*file, name string, settings []FileSetting) []*file {
-	f := &file{
+// AttachReader attaches a file using an io.Reader
+func (m *Message) AttachReader(name string, r io.Reader, settings ...FileSetting) {
+	m.attachments = m.appendFile(m.attachments, fileFromReader(name, r), settings)
+}
+
+// Attach attaches the files to the email.
+func (m *Message) Attach(filename string, settings ...FileSetting) {
+	m.attachments = m.appendFile(m.attachments, fileFromFilename(filename), settings)
+}
+
+// EmbedReader embeds the images to the email.
+func (m *Message) EmbedReader(name string, r io.Reader, settings ...FileSetting) {
+	m.embedded = m.appendFile(m.embedded, fileFromReader(name, r), settings)
+}
+
+// Embed embeds the images to the email.
+func (m *Message) Embed(filename string, settings ...FileSetting) {
+	m.embedded = m.appendFile(m.embedded, fileFromFilename(filename), settings)
+}
+
+func fileFromFilename(name string) *file {
+	return &file{
 		Name:   filepath.Base(name),
 		Header: make(map[string][]string),
 		CopyFunc: func(w io.Writer) error {
@@ -299,7 +331,22 @@ func (m *Message) appendFile(list []*file, name string, settings []FileSetting)
 			return h.Close()
 		},
 	}
+}
 
+func fileFromReader(name string, r io.Reader) *file {
+	return &file{
+		Name:   filepath.Base(name),
+		Header: make(map[string][]string),
+		CopyFunc: func(w io.Writer) error {
+			if _, err := io.Copy(w, r); err != nil {
+				return err
+			}
+			return nil
+		},
+	}
+}
+
+func (m *Message) appendFile(list []*file, f *file, settings []FileSetting) []*file {
 	for _, s := range settings {
 		s(f)
 	}
@@ -310,13 +357,3 @@ func (m *Message) appendFile(list []*file, name string, settings []FileSetting)
 
 	return append(list, f)
 }
-
-// Attach attaches the files to the email.
-func (m *Message) Attach(filename string, settings ...FileSetting) {
-	m.attachments = m.appendFile(m.attachments, filename, settings)
-}
-
-// Embed embeds the images to the email.
-func (m *Message) Embed(filename string, settings ...FileSetting) {
-	m.embedded = m.appendFile(m.embedded, filename, settings)
-}

vendor/gopkg.in/mail.v2/mime.go

@@ -1,6 +1,6 @@
 // +build go1.5
 
-package gomail
+package mail
 
 import (
 	"mime"

vendor/gopkg.in/mail.v2/mime_go14.go

@@ -1,6 +1,6 @@
 // +build !go1.5
 
-package gomail
+package mail
 
 import "gopkg.in/alexcesaro/quotedprintable.v3"
 

vendor/gopkg.in/mail.v2/send.go

@@ -1,10 +1,10 @@
-package gomail
+package mail
 
 import (
 	"errors"
 	"fmt"
 	"io"
-	"net/mail"
+	stdmail "net/mail"
 )
 
 // Sender is the interface that wraps the Send method.
@@ -36,7 +36,7 @@ func (f SendFunc) Send(from string, to []string, msg io.WriterTo) error {
 func Send(s Sender, msg ...*Message) error {
 	for i, m := range msg {
 		if err := send(s, m); err != nil {
-			return fmt.Errorf("gomail: could not send email %d: %v", i+1, err)
+			return &SendError{Cause: err, Index: uint(i)}
 		}
 	}
 
@@ -108,7 +108,7 @@ func addAddress(list []string, addr string) []string {
 }
 
 func parseAddress(field string) (string, error) {
-	addr, err := mail.ParseAddress(field)
+	addr, err := stdmail.ParseAddress(field)
 	if err != nil {
 		return "", fmt.Errorf("gomail: invalid address %q: %v", field, err)
 	}

vendor/gopkg.in/mail.v2/smtp.go

@@ -1,4 +1,4 @@
-package gomail
+package mail
 
 import (
 	"crypto/tls"
@@ -27,23 +27,39 @@ type Dialer struct {
 	// most cases since the authentication mechanism should use the STARTTLS
 	// extension instead.
 	SSL bool
-	// TSLConfig represents the TLS configuration used for the TLS (when the
+	// TLSConfig represents the TLS configuration used for the TLS (when the
 	// STARTTLS extension is used) or SSL connection.
 	TLSConfig *tls.Config
+	// StartTLSPolicy represents the TLS security level required to
+	// communicate with the SMTP server.
+	//
+	// This defaults to OpportunisticStartTLS for backwards compatibility,
+	// but we recommend MandatoryStartTLS for all modern SMTP servers.
+	//
+	// This option has no effect if SSL is set to true.
+	StartTLSPolicy StartTLSPolicy
 	// LocalName is the hostname sent to the SMTP server with the HELO command.
 	// By default, "localhost" is sent.
 	LocalName string
+	// Timeout to use for read/write operations. Defaults to 10 seconds, can
+	// be set to 0 to disable timeouts.
+	Timeout time.Duration
+	// Whether we should retry mailing if the connection returned an error,
+	// defaults to true.
+	RetryFailure bool
 }
 
 // NewDialer returns a new SMTP Dialer. The given parameters are used to connect
 // to the SMTP server.
 func NewDialer(host string, port int, username, password string) *Dialer {
 	return &Dialer{
-		Host:     host,
-		Port:     port,
-		Username: username,
-		Password: password,
-		SSL:      port == 465,
+		Host:         host,
+		Port:         port,
+		Username:     username,
+		Password:     password,
+		SSL:          port == 465,
+		Timeout:      10 * time.Second,
+		RetryFailure: true,
 	}
 }
 
@@ -55,10 +71,15 @@ func NewPlainDialer(host string, port int, username, password string) *Dialer {
 	return NewDialer(host, port, username, password)
 }
 
+// NetDialTimeout specifies the DialTimeout function to establish a connection
+// to the SMTP server. This can be used to override dialing in the case that a
+// proxy or other special behavior is needed.
+var NetDialTimeout = net.DialTimeout
+
 // Dial dials and authenticates to an SMTP server. The returned SendCloser
 // should be closed when done using it.
 func (d *Dialer) Dial() (SendCloser, error) {
-	conn, err := netDialTimeout("tcp", addr(d.Host, d.Port), 10*time.Second)
+	conn, err := NetDialTimeout("tcp", addr(d.Host, d.Port), d.Timeout)
 	if err != nil {
 		return nil, err
 	}
@@ -72,14 +93,25 @@ func (d *Dialer) Dial() (SendCloser, error) {
 		return nil, err
 	}
 
+	if d.Timeout > 0 {
+		conn.SetDeadline(time.Now().Add(d.Timeout))
+	}
+
 	if d.LocalName != "" {
 		if err := c.Hello(d.LocalName); err != nil {
 			return nil, err
 		}
 	}
 
-	if !d.SSL {
-		if ok, _ := c.Extension("STARTTLS"); ok {
+	if !d.SSL && d.StartTLSPolicy != NoStartTLS {
+		ok, _ := c.Extension("STARTTLS")
+		if !ok && d.StartTLSPolicy == MandatoryStartTLS {
+			err := StartTLSUnsupportedError{
+				Policy: d.StartTLSPolicy}
+			return nil, err
+		}
+
+		if ok {
 			if err := c.StartTLS(d.tlsConfig()); err != nil {
 				c.Close()
 				return nil, err
@@ -111,7 +143,7 @@ func (d *Dialer) Dial() (SendCloser, error) {
 		}
 	}
 
-	return &smtpSender{c, d}, nil
+	return &smtpSender{c, conn, d}, nil
 }
 
 func (d *Dialer) tlsConfig() *tls.Config {
@@ -121,6 +153,47 @@ func (d *Dialer) tlsConfig() *tls.Config {
 	return d.TLSConfig
 }
 
+// StartTLSPolicy constants are valid values for Dialer.StartTLSPolicy.
+type StartTLSPolicy int
+
+const (
+	// OpportunisticStartTLS means that SMTP transactions are encrypted if
+	// STARTTLS is supported by the SMTP server. Otherwise, messages are
+	// sent in the clear. This is the default setting.
+	OpportunisticStartTLS StartTLSPolicy = iota
+	// MandatoryStartTLS means that SMTP transactions must be encrypted.
+	// SMTP transactions are aborted unless STARTTLS is supported by the
+	// SMTP server.
+	MandatoryStartTLS
+	// NoStartTLS means encryption is disabled and messages are sent in the
+	// clear.
+	NoStartTLS = -1
+)
+
+func (policy *StartTLSPolicy) String() string {
+	switch *policy {
+	case OpportunisticStartTLS:
+		return "OpportunisticStartTLS"
+	case MandatoryStartTLS:
+		return "MandatoryStartTLS"
+	case NoStartTLS:
+		return "NoStartTLS"
+	default:
+		return fmt.Sprintf("StartTLSPolicy:%v", *policy)
+	}
+}
+
+// StartTLSUnsupportedError is returned by Dial when connecting to an SMTP
+// server that does not support STARTTLS.
+type StartTLSUnsupportedError struct {
+	Policy StartTLSPolicy
+}
+
+func (e StartTLSUnsupportedError) Error() string {
+	return "gomail: " + e.Policy.String() + " required, but " +
+		"SMTP server does not support STARTTLS"
+}
+
 func addr(host string, port int) string {
 	return fmt.Sprintf("%s:%d", host, port)
 }
@@ -139,12 +212,29 @@ func (d *Dialer) DialAndSend(m ...*Message) error {
 
 type smtpSender struct {
 	smtpClient
-	d *Dialer
+	conn net.Conn
+	d    *Dialer
+}
+
+func (c *smtpSender) retryError(err error) bool {
+	if !c.d.RetryFailure {
+		return false
+	}
+
+	if nerr, ok := err.(net.Error); ok && nerr.Timeout() {
+		return true
+	}
+
+	return err == io.EOF
 }
 
 func (c *smtpSender) Send(from string, to []string, msg io.WriterTo) error {
+	if c.d.Timeout > 0 {
+		c.conn.SetDeadline(time.Now().Add(c.d.Timeout))
+	}
+
 	if err := c.Mail(from); err != nil {
-		if err == io.EOF {
+		if c.retryError(err) {
 			// This is probably due to a timeout, so reconnect and try again.
 			sc, derr := c.d.Dial()
 			if derr == nil {
@@ -154,6 +244,7 @@ func (c *smtpSender) Send(from string, to []string, msg io.WriterTo) error {
 				}
 			}
 		}
+
 		return err
 	}
 
@@ -182,9 +273,8 @@ func (c *smtpSender) Close() error {
 
 // Stubbed out for tests.
 var (
-	netDialTimeout = net.DialTimeout
-	tlsClient      = tls.Client
-	smtpNewClient  = func(conn net.Conn, host string) (smtpClient, error) {
+	tlsClient     = tls.Client
+	smtpNewClient = func(conn net.Conn, host string) (smtpClient, error) {
 		return smtp.NewClient(conn, host)
 	}
 )

vendor/gopkg.in/mail.v2/writeto.go

@@ -1,4 +1,4 @@
-package gomail
+package mail
 
 import (
 	"encoding/base64"
@@ -19,8 +19,8 @@ func (m *Message) WriteTo(w io.Writer) (int64, error) {
 }
 
 func (w *messageWriter) writeMessage(m *Message) {
-	if _, ok := m.header["Mime-Version"]; !ok {
-		w.writeString("Mime-Version: 1.0\r\n")
+	if _, ok := m.header["MIME-Version"]; !ok {
+		w.writeString("MIME-Version: 1.0\r\n")
 	}
 	if _, ok := m.header["Date"]; !ok {
 		w.writeHeader("Date", m.FormatDate(now()))
@@ -28,15 +28,15 @@ func (w *messageWriter) writeMessage(m *Message) {
 	w.writeHeaders(m.header)
 
 	if m.hasMixedPart() {
-		w.openMultipart("mixed")
+		w.openMultipart("mixed", m.boundary)
 	}
 
 	if m.hasRelatedPart() {
-		w.openMultipart("related")
+		w.openMultipart("related", m.boundary)
 	}
 
 	if m.hasAlternativePart() {
-		w.openMultipart("alternative")
+		w.openMultipart("alternative", m.boundary)
 	}
 	for _, part := range m.parts {
 		w.writePart(part, m.charset)
@@ -77,8 +77,11 @@ type messageWriter struct {
 	err        error
 }
 
-func (w *messageWriter) openMultipart(mimeType string) {
+func (w *messageWriter) openMultipart(mimeType, boundary string) {
 	mw := multipart.NewWriter(w)
+	if boundary != "" {
+		mw.SetBoundary(boundary)
+	}
 	contentType := "multipart/" + mimeType + ";\r\n boundary=" + mw.Boundary()
 	w.writers[w.depth] = mw
 
@@ -158,7 +161,11 @@ func (w *messageWriter) Write(p []byte) (int, error) {
 }
 
 func (w *messageWriter) writeString(s string) {
-	n, _ := io.WriteString(w.w, s)
+	if w.err != nil { // do nothing when in error
+		return
+	}
+	var n int
+	n, w.err = io.WriteString(w.w, s)
 	w.n += int64(n)
 }
 

vendor/vendor.json

@@ -129,10 +129,10 @@
 			"revisionTime": "2015-07-16T17:19:45Z"
 		},
 		{
-			"checksumSHA1": "iq5WdjScmTU+LfNoerLuwcnXpdM=",
-			"path": "gopkg.in/gomail.v2",
-			"revision": "81ebce5c23dfd25c6c67194b37d3dd3f338c98b1",
-			"revisionTime": "2016-04-11T21:29:32Z"
+			"checksumSHA1": "SoHkt4HLtGvg9wZIDX6BJTqkDgs=",
+			"path": "gopkg.in/mail.v2",
+			"revision": "f59b9b83a4e522098e3d3eb94e6f81850ad6e973",
+			"revisionTime": "2018-11-12T22:01:18Z"
 		},
 		{
 			"checksumSHA1": "12GqsW8PiRPnezDDy0v4brZrndM=",