Most UNIX mail server support recipient delimiters behind a plus sign in email addresses.
In the above example "everything" could be any string, and the mail should get into the mail box of the user "user".
In postfix it is called recipient_delimiter:
Is this possible with Exchange 2010?
Usecase1: The user can use different email addresses. He can use email@example.com for the communication with "fooshop". If he gets spam mail to this address later, he knows that fooshop has given his address to someone else.
Usecase2: We run a ticket system ( http://tbz-pariv.de/software/modwork/ ) and want to add send scans via email to the system. The network scanner can only modify the to-address and we want to insert the ticket type like this firstname.lastname@example.org