12. A non-transitory computer-readable storage medium having stored thereon computer instructions that, upon execution by one or more processors, at least cause a computing system to: process, for emails received, email header information to identify a first email conversation comprising a first email and replies to the first email; identify 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 the 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; generating a user interface listing emails received for a first user, the user interface listing emails identifying that an email is associated with a first email conversation that was previously linked to a second email conversation by a second user; present a user interface displaying the first email conversation and the second email conversation; receive input from a first user selecting an email in the first email conversation; display an indication the selected email is in the first email conversation that was associated with the second email conversation by the second user; receive 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; store data identifying that the first user has linked the first email conversation to the second email conversation.
13. The non-transitory computer-readable storage medium of claim 12 , wherein generating a user interface listing emails received for a first user, the user interface identifying that an email is associated with a first email conversation that was previously linked to a second email conversation by a second user, comprises generating a user interface displaying text indicating that the email is associated with a first email conversation that was previously linked to a second email conversation by another user.