Encoding data in email headers

An electronic communication system comprising:

• one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising:
• receiving an indication to associate a first action with information in a first email message,
• generating the first email message including a Message-ID field including first encoded data identifying the first action,
• transmitting the first email message that includes the Message-ID field including the first encoded data identifying the first action, wherein the first encoded data in the Message-ID field is encrypted so that the first encoded data is only interpretable by one or more authorized recipients, and
• receiving a second email message that includes an In-Reply-To field containing encrypted encoded data from another email message and, when the electronic communication system is associated with an authorized recipient of the second email message, decrypting the encrypted encoded data in the In-Reply-To field to extract second encoded data and processing the second email message based on the second encoded data including deriving a second action to be carried out from the second encoded data and carrying out the second action.