1. A computer-implemented method for linking email conversations, comprising: processing, for emails received by a first user, email header information to identify a first email conversation comprising a first email and replies to the first email; identifying that one or more emails in the first email conversation has an associated identifier indicating the first email conversation was associated by a second user with a second email conversation comprising a second email and replies to the second email, wherein identifying that one or more emails in the first email conversation has an associated identifier indicating the first email conversation was associated by the second user with a second email conversation comprises identifying a group identifier in email header information is associated with emails in the first email conversation and with emails in the second email conversation; presenting a user interface displaying the first email conversation and the second email conversation; receiving input selecting an email in the first email conversation; displaying an indication the selected email is in the first email conversation that was associated with the second email conversation by the second user; receiving input from the first user and based on the indication, the input specifying to create a link between the first email conversation and the second email conversation; and storing data indicating the first user has established the link between the first email conversation and the second email conversation.
2. The computer-implemented method of claim 1 , wherein processing email header information to identify a first email conversation comprises identifying emails listed in a header references field.