Building an email in Golang to be delivered using Amazon SES

email.go

func buildEmailInput(source, destination, subject, message string,
	csvFile []byte) (*ses.SendRawEmailInput, error) {

	buf := new(bytes.Buffer)
	writer := multipart.NewWriter(buf)

	// email main header:
	h := make(textproto.MIMEHeader)
	h.Set("From", source)
	h.Set("To", destination)
	h.Set("Return-Path", source)
	h.Set("Subject", subject)
	h.Set("Content-Language", "en-US")
	h.Set("Content-Type", "multipart/mixed; boundary=\""+writer.Boundary()+"\"")
	h.Set("MIME-Version", "1.0")
	_, err := writer.CreatePart(h)
	if err != nil {
		return nil, err
	}

	// body:
	h = make(textproto.MIMEHeader)
	h.Set("Content-Transfer-Encoding", "7bit")
	h.Set("Content-Type", "text/plain; charset=us-ascii")
	part, err := writer.CreatePart(h)
	if err != nil {
		return nil, err
	}
	_, err = part.Write([]byte(message))
	if err != nil {
		return nil, err
	}

	// file attachment:
	fn := attachmentFilename
	h = make(textproto.MIMEHeader)
	h.Set("Content-Disposition", "attachment; filename="+fn)
	h.Set("Content-Type", "text/csv; x-unix-mode=0644; name=\""+fn+"\"")
	h.Set("Content-Transfer-Encoding", "7bit")
	part, err = writer.CreatePart(h)
	if err != nil {
		return nil, err
	}
	_, err = part.Write(csvFile)
	if err != nil {
		return nil, err
	}
	err = writer.Close()
	if err != nil {
		return nil, err
	}

	// Strip boundary line before header (doesn't work with it present)
	s := buf.String()
	if strings.Count(s, "\n") < 2 {
		return nil, fmt.Errorf("invalid e-mail content")
	}
	s = strings.SplitN(s, "\n", 2)[1]

	raw := ses.RawMessage{
		Data: []byte(s),
	}
	input := &ses.SendRawEmailInput{
		Destinations: []*string{aws.String(destination)},
		Source:       aws.String(source),
		RawMessage:   &raw,
	}

	return input, nil
}

line 38 should be h.Set("Content-Disposition", "attachment; filename=""+fn+""").
Else this fails if file name has chars like @
Though, thanks for the ready made code.

you may be better using the help of https://pkg.go.dev/github.com/jhillyerd/enmime

You build the email with enmime.EmailBuilder, then get the thing with the .Build attach method and use a buffer from bytes to enmime.Part.Encode the entire thing into the buffer, then you can use that to get the bytes back.

easy peasy!

I am unable to send attachment with file type other than text/csv. Can anyone please help!!!

be explicit about any error messages or panics, maybe?

I am unable to send attachment with file type other than text/csv. Can anyone please help!!!

be explicit about any error messages or panics, maybe?

When I try to send a jpeg image with Content-Type value image/jpeg I am getting a Serialization Error with status code 500.

@rishab-zomato better use the library I'm linking on here