Apple Mail inbox multiplying at an alarming rate

Question

All of a sudden, this morning, Apple Mail started downloading emails to my gmail account despite the fact that I knew there were no new emails. I looked at the inbox and discovered that there were four copies of each of the recent email. I cancelled the sync, and Mail promptly started to sync twice as many emails. After a few attempts I had approximately 32 times my inbox preparing to sync, so I closed Mail and left this way.

Does anyone know what happened, why, and, most importantly, how to fix it?

EDIT: After restarting Mail the problem has gone away. However, I still want to know what happened and how to stop it from happening again.

Answer 1

Many people had this problem. The only explanation is a bug in the Mail program. You are lucky that in your case the remedy was as simple as restarting Mail. Other people had to monkey with thrashed Mail files. The google query Apple Mail emails duplicated returns 1,330,000 results!

If you would like to read about other people's problems in that respect and their solutions, some of the references I found are :

Mail.app: Duplicate Messages
OS 10.6 - Mail is showing duplicated incoming messages !
Duplicate emails pulled from server each time mail is checked
Snow Leopard-Exchange Mail: duplicate messages

There is no common grounds between the cases, and in most cases a trivial manipulation of some file of Mail was enough to kick it back into working condition.

If you keep on having problems with Mail, I could suggest moving to some other mail client (such as Thunderbird).