In email-to case, duplicate cases are created when the email is sent/cc'd several addresses (cc).
When I send an email to the email-to-case address AND to another person (in the cc of the mail), it creates 3 cases in Salesforce. (I don't know why 3… and the 3rd one is created several minutes after the first 2).
If I send an email only to the email-to-case address, it creates only one case.
Do you know how I can avoid this duplicate case?
* EDIT *
After some other tests, I see that some cases without cc are also created with duplicate… so it is not not the reason of the problem.
I tested to use the big email adress of the email to case (the normal email adress of the email to case redirect to this big email adress) and then I havn't the duplicate problem.
Best Answer
See the comments below this post: Email To Case - Duplicate Cases. I believe it provides a solution and answers your question on how to resolve the problem you are having.
You'll want to implement your Email Service with the appropriate Apex code logic, mainly adapted from the following post: http://sforcehacks.blogspot.co.il/2012/01/email-to-case-can-create-too-many-cases.html