This is a very commonly occurring problem in outlook/outlook express where you start receiving same email message multiple times.

First log into your email account using your webmail interface and verify that there is only one copy of each message in your mail box and not multiple copies. If there is only one copy of each email message in your inbox, and yet you are receiving multiple copies, it means that your email client (viz. outlook) is downloading the same message again and again.

When you are downloading emails from a POP3 mail server, the mail server does not decide which pieces of emails you have already download earlier. This information is recorded only by your email client viz. outlook/outlook express (or any other email client such as Windows Live Mail or Mozilla Thunderbird). Below are the most common causes of this issue and how you can resolve it:

1. If you have setup your mail client to leave messages on the serverthen it is the job of Outlook to remember what messages it has already downloaded. The mail server does not remember which message you downloaded. This is the reason why you can download same messages at the office, leave them on the server and download them again at home in your home computer. If the server remembered which messages had been downloaded, then they would not download again to another machine. Each instance of Outlook on each machine must remember what it has already downloaded.

   For remembering which messages Outlook already downloaded, it keeps a list of the message IDs for the messages it downloaded successfully. Next time when it checks for new messages, it gets a list of all the message IDs on the server, compares it to the list or message IDs it has already recorded as been downloaded, and requests only those messages that have not yet been downloaded. If the list of downloaded message IDs becomes corrupted, which is common especially when that list gets long, Outlook loses track and starts downloading all messages over and over again.

   To resolve this issue, Un-check leave messages on the server and then Send and receive to get the server mailbox cleaned out. You can then re-check it. I suggest you only leave messages on the server for 10 or 15 days, depending on your mail usage. However, if you still wish to leave a copy of all messages on the server, then it is advisable to connect from your outlook via IMAP and not POP3.

2. When outlook is downloading new messages from the email server, it first downloads all new messages and after that updates its local list of downloaded message IDs. Often, what happens is that an email message gets stuck during the download process. This causes your send/receive session to terminate without updating the local list of received messages, or without deleting received messages from the server (if outlook was set to delete messages on the server after downloading.

   Messages can get stuck due to various reasons, some of which are mentioned below:

   1. They are corrupted or crafted to contain special characters that cause your email client program to terminate.
   2. Large messages take so long to send or receive that your email program starts another send/receive process before the last session is complete.
   3. Large messages take so long to send or receive that you interrupt the process before it is complete.

3. To resolve such a situation, log into your email account via the webmail interface and move the messages from your inbox to another temporarily created folder. Then start moving messages back to your inbox one or a few at a time, and downloading them to Outlook until you find the message causing the problem. Manage problem messages through webmail. You can either move the problem messages to a folder other than inbox or delete them permanently.

4. Some users setup their email client to check for new messages too frequently. They usually set it to check every minute. The most recommended time gap between two subsequent checks is 15 mintues. Checking more frequently, i.e. at smaller time intervals, can often result in the next check beginning before the last one ends. When this happens, the index file of the e-mail client will no longer be synchronized with the email server, resulting in multiple copies of the same message.

   To correct his issue, change the setting of your outlook so that it automatically checks for new email messages at no less than 15 minutes interval. You can manually force a check if needed, but be sure the last check has completely finished.