code: private MimeMessage buildMsg() throws MessagingException {
  		final Charset charset = this.mailAccount.getCharset();
  		final MimeMessage msg = new MimeMessage(getSession(this.useGlobalSession));
  		// 发件人
  		final String from = this.mailAccount.getFrom();
  		if (StrUtil.isEmpty(from)) {
  			// 用户未提供发送方，则从Session中自动获取
  			msg.setFrom();
  		} else {
  			msg.setFrom(InternalMailUtil.parseFirstAddress(from, charset));
  		}
  		// 标题
  		msg.setSubject(this.title, charset.name());
  		// 发送时间
  		msg.setSentDate(new Date());
  		// 内容和附件
  		msg.setContent(buildContent(charset));
  		// 收件人
  		msg.setRecipients(MimeMessage.RecipientType.TO, InternalMailUtil.parseAddressFromStrs(this.tos, charset));
  		// 抄送人
  		if (ArrayUtil.isNotEmpty(this.ccs)) {
  			msg.setRecipients(MimeMessage.RecipientType.CC, InternalMailUtil.parseAddressFromStrs(this.ccs, charset));
  		}
  		// 密送人
  		if (ArrayUtil.isNotEmpty(this.bccs)) {
  			msg.setRecipients(MimeMessage.RecipientType.BCC, InternalMailUtil.parseAddressFromStrs(this.bccs, charset));
  		}
  		return msg;
  	}
docs: 构建消息
  
  @return {@link MimeMessage}消息
  @throws MessagingException 消息异常