获取某一天的邮件：
` public static void main(String[] args) throws Exception {
Properties props = new Properties();
props.put("mail.transport.protocol", "smtp");
props.put("mail.store.protocol", "imap");
props.put("mail.smtp.class", "com.sum.mail.smtp.SMTPTransport");
props.put("mail.imap.class", "com.sum.mail.imap.IMAPStore");
props.put("mail.smtp.host", "pop.163.com");
Session session = Session.getInstance(props);
Store store = session.getStore("pop3");
store.connect("pop.163.com", "xxx", "xxx");
Folder folder = store.getFolder("inbox");
folder.open(Folder.READ_ONLY);
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
Date date = simpleDateFormat.parse("2021-10-01");
Date date2 = simpleDateFormat.parse("2021-10-02");
SearchTerm comparisonTermGe = new SentDateTerm(DateTerm.GE, date);
SearchTerm comparisonTermLt = new SentDateTerm(DateTerm.LT, date2);
SearchTerm comparisonAndTerm = new AndTerm(comparisonTermGe, comparisonTermLt);
Message[] messages = folder.search(comparisonAndTerm);
System.out.println("你一共有" + messages.length + "封邮件");
System.out.println("==============================================");
for (int i = 0; i < messages.length; i++) {
System.out.println("==============================================");
Message message = messages[i];
System.out.println("邮件主题" + message.getSubject());
System.out.println("发送日期" + message.getSentDate());
System.out.println("邮件内容" + message.getContentType());
//System.out.println("邮件内容2" + message.getContent());
}
folder.close(false);
store.close();
}`
