According to ARMA, formerly known as the Association of Records Managers and Administrators, records and information management (RIM) is defined as “the field of management responsible for establishing and implementing policies, systems, and procedures to capture, create, access, distribute, use, store, secure, retrieve, and ensure disposition of an organization's records and information.”
Information is considered a record if it was created, received, and maintained as evidence and information by an organization or person, in pursuance of legal obligations or during a business transaction. Examples of records include:
The specific criteria should be based on your own company policies and industry standards, particularly if it’s a tightly regulated sector. The amount of files that are records will vary based on industry and job function, with heavily regulated industries like pharmaceuticals and financial services providers having higher numbers of records. Colleagues working in legal or finance have a higher number files that are records than someone who works in helpdesk support.
In short, emails are simply a specific format of information, and if an email meets the criteria above, it is considered a record.
Sometimes the best way to figure out which emails are records is to remove all those that are definitely not records. Most emails are transitory and only meaningful or useful for a brief period of time. Examples of these emails include, meeting invitations, announcements, itineraries, drafts, requests for information, duplicates, and notifications.
The remainder of emails are those that have value–administrative value, such as documenting that formal reviews have taken place per policy; financial and legal value, such as pricing, terms, and verbal agreements; and historical or long-term management value, such as board meetings, high-level management meeting materials, particularly when decisions are made.
So, an email should be retained if it is a record, i.e., information needed to run the organization.