help

These days , I have tried develop an email client to check email and display it, it can work fine in normal cases, but when there are a lot of emails in server and also in locally, it is very slow to retrieve mails, what I do is listed below:

1. get messages from mail server
2. compare the message ID with local mails
3. if it is new, then save the mail locally
4. then display all the mails

Do you have any suggesions for improving the performance,thanks in advance.