docs: public MailAccount defaultIfEmpty() {
  		// 去掉发件人的姓名部分
  		final String fromAddress = InternalMailUtil.parseFirstAddress(this.from, this.charset).getAddress();
  
  		if (StrUtil.isBlank(this.host)) {
  			// 如果SMTP地址为空，默认使用smtp.<发件人邮箱后缀>
  			this.host = StrUtil.format("smtp.{}", StrUtil.subSuf(fromAddress, fromAddress.indexOf('@') + 1));
  		}
  		if (StrUtil.isBlank(user)) {
  			// 如果用户名为空，默认为发件人邮箱前缀
  			this.user = StrUtil.subPre(fromAddress, fromAddress.indexOf('@'));
  		}
  		if (null == this.auth) {
  			// 如果密码非空白，则使用认证模式
  			this.auth = (false == StrUtil.isBlank(this.pass));
  		}
  		if (null == this.port) {
  			// 端口在SSL状态下默认与socketFactoryPort一致，非SSL状态下默认为25
  			this.port = (null != this.sslEnable && this.sslEnable) ? this.socketFactoryPort : 25;
  		}
  		if (null == this.charset) {
  			// 默认UTF-8编码
  			this.charset = CharsetUtil.CHARSET_UTF_8;
  		}
  
  		return this;
  	}