为带有附件的电子邮件设置多部分

从我的应用程序中，我发送带有附件的邮件。完整的代码在这里

public int sendMail(MailDraft mailDraftInstance, mailInstance, path){                               //Send the mail
    String mailSubject  = mailDraftInstance.subject
    String toAddress    = mailDraftInstance.toAddress
    String ccAddress    = mailDraftInstance.ccAddress
    String bccAddress   = mailDraftInstance.bccAddress
    String fromAddress  = mailDraftInstance.fromAddress
    String body         = mailDraftInstance.body

    String smtpUsername = 'myusername'
    String smtpPassword = 'mypwd'

    /*** set the SMTP properties and Authenticate*****/
    Properties smtpMailProperties
    Session mailSession
    smtpMailProperties = mailInstance.getSmtpConnectionProperties()
    mailSession = mailInstance.getMailSession(smtpMailProperties, smtpUsername, smtpPassword)

    try {

        /**** Set the Header *************/
        User loggedInUser = User.get(SecurityContextHolder.context.authentication.principal.id)
        Address address = new InternetAddress(mailDraftInstance.fromAddress);
        Address replyAddress = new InternetAddress(mailDraftInstance.fromAddress);
        Message message = new MimeMessage(mailSession);
        message.setFrom(address); 
        //message.addFrom(address); //Set the from address with the logged in user email
        message.setReplyTo(replyAddress)

        /*** set Recipients*********/
        String recipientType = 'TO'
        setMailRecipients(message, toAddress, recipientType, toAddressError)
        recipientType = 'CC'
        setMailRecipients(message, ccAddress, recipientType, ccAddressError)
        recipientType = 'BCC'
        setMailRecipients(message, bccAddress, recipientType, bccAddressError)

        message.setSubject(mailSubject);    

        Multipart multiPart = new MimeMultipart("alternative");   // Create an "Alternative" Multipart message
        // Multipart multiPart = new MimeMultipart("mixed");


        MimeBodyPart text = new MimeBodyPart();
        MimeBodyPart html = new MimeBodyPart();

        text.setText(body.replaceAll("\\<[^>]*>","").replaceAll("&nbsp;"," ").replaceAll("&amp;","&"));  //set the text/plain version
        html.setContent(Jsoup.parse(body).html(), "text/html");     //set the text/html version

        multiPart.addBodyPart(text);
        multiPart.addBodyPart(html);


        /*  // Set the Body 
        Multipart multiPart = new MimeMultipart();
        MimeBodyPart messageHtml = new MimeBodyPart();  //Create a mime body 
        messageHtml.setContent(body, "text/html");      //set the content type as HTML
        multiPart.addBodyPart(messageHtml);*/

        // Add the Attachments
        if(!mailDraftInstance.attachments.isEmpty()){
            Mail.attachFiles(mailDraftInstance.attachments, multiPart, path)
        }  
        int i=0;
        mailDraftInstance.attachments.each{
            i++
        }
        message.setContent(multiPart);      //set the content
        Transport.send(message);            //send the mail
    }catch (Exception e) {
        if(e instanceof AddressException){
            println "Email Recipient Address error"                             //Error with the TO Or CC Or BCC Adresss
            return addressErrorType
        }else{
            println e                                                           //Other errors, may be with the SMTP server
            println "Cannot send email as an error occurred"
            return addressErrorType
        }
    }
    return mailSentSuccessfully    //mail sent successfully
}



  public static attachFiles(def attachments, Multipart multiPart, String path){                     //Attach files
    attachments.each {

        def attachmentId = it.id
        String newFile= TrainingService.createFile(attachmentId, path)

        MimeBodyPart fileAttachmentPart = new MimeBodyPart();
        FileDataSource attachmentfile = new FileDataSource(newFile);
        fileAttachmentPart.setDataHandler(new DataHandler(attachmentfile));
        println "newFile============="+attachmentfile.getName()
        fileAttachmentPart.setFileName(attachmentfile.getName());
        multiPart.addBodyPart(fileAttachmentPart);

    }

}

如果我设置

  Multipart multiPart = new MimeMultipart("alternative"); 

一些客户端（yahoomail）收不到附件。

那么应该使用多部分设置来接收包含文本、html 和附件的电子邮件吗？

如果您希望邮件同时包含备用部分和附件，则需要两个多部分，一个嵌套在另一个中。外部多部分应该是多部分/混合的。该多部分的第一个主体部分应该是多部分/替代部分。外部多部分的第二个主体部分应该是附件。内部多部分包含纯文本和 html 正文部分。