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Why am I receiving duplicate copies of email messages, and how do I stop it?

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Possible reasons for receiving multiple copies of email messages include:

Mail forwarding loops

Symptoms

Most often, a mail forwarding loop prevents you from receiving any mail, causing mail sent to you to bounce back to the sender. However, if you receive many copies of every email message, a forwarding loop may be the cause of this as well.

Explanation

If you forward your email from one computer to another, it is possible to set up the forwarding in such a way that there is no final destination for your email messages.

For example, suppose you have accounts on two computers named Coffee and Tea. If you set mail forwarding on Coffee to forward mail to Tea, and set forwarding on Tea to forward mail to Coffee, you create a mail forwarding loop. Mail sent to Coffee would go to Tea instead, but when Tea got it, it would send it right back to Coffee. The mail would never have a final delivery location.

Solution

To fix this problem, change your mail forwarding so that all mail messages, no matter what address they are sent to, have a final destination. See At IU, how do I forward my email?

Multiple subscriptions to a mailing list

If you are receiving duplicate messages from only a single mailing list, you might be subscribed to that list more than once. Request to see the subscriber list and examine it. Look for multiple occurrences of your email address, as well as the addresses of other mailing lists you receive. Mailing lists frequently subscribe to other mailing lists.

Network and server problems

Symptoms

If you are receiving duplicates of only some of your mail, the cause may be technical difficulty along the delivery path. Either a network connection is having problems, or one of the computers along the route is very slow or having other system problems.

Explanation

Most mail delivery protocols and programs are conservative. If they are unsure whether a mail message was successfully passed along to the next computer on the network, the sender will try to send it again. If the message was passed along successfully the first time, the second attempt will produce a second copy of the same message, and you will likely receive both copies.

On large networks such as the Internet, a mail message must usually pass through several different computers before it reaches its final destination. This problem can potentially occur at any computer along the way.

A synchronization problem in the SMTP mail delivery protocol, which is used by most mail programs on the Internet, can make this error more likely; see the Internet RFC document Duplicate Messages and SMTP.

No solution

Unfortunately, this problem has no real solution, except to wait until the problem on the network is resolved. If this problem is chronic and doesn't seem to be associated with a more general network or computer problem, the mail delivery software on the computer in question may be misconfigured. In this case, contact the administrator of the computer.

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Last modified on February 19, 2013.

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