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

On this page:

• Mail forwarding loops
• Multiple subscriptions to a mailing list
• Network and server problems

Possible reasons for receiving multiple copies of email messages:

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.

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. For information on how to solve this problem, see Why am I receiving two copies of messages sent to a LISTSERV mailing list?

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.

The SMTP mail delivery protocol, which is used by most mail programs on the Internet, has a specific "weak point" in it that can make this situation more likely to happen. For more information on this problem, see the Internet RFC document Duplicate Messages and SMTP.

No solution

Unfortunately, there is no real solution to this, 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, it is possible that the mail delivery software on the computer in question is misconfigured. In this case, contact the administrator of the computer.

Also see:

• Why am I receiving two copies of messages sent to a LISTSERV mailing list?
• In Microsoft Outlook 2000 and later for Windows, how do I automatically forward all of my mail to another address?
• How do I forward my mail from a Unix account?
• Why do I sometimes not receive mail from distribution lists when other users on the same distribution lists do?
• What does the "too many hops" error mean when an email message I send fails?
• At IU, how do I forward my email?