The decision creates a potential legal minefield for the terms of staff contracts and an administrative nightmare for IT teams running email servers, back up and storage.
The judge ruled businesses do not have an "enforceable proprietary claim" to staff email content unless that content can be considered to be confidential information belonging to a business, unless business copyright applies to the content, or unless the business has a contractual right of ownership over the content.
Ruling in the case involving Fairstar Heavy Transport and its former chief executive, Justice Edwards-Stewart said: "I can find no practical basis for holding that there should be property in the content of an email, even if I thought that it was otherwise open to me to do so.
"To the extent that people require protection against the misuse of information contained in emails, in my judgment satisfactory protection is provided under English law either by the equitable jurisdiction to which I have referred in relation to confidential information (or by contract, where there is one) or, where applicable, the law of copyright.
"There are no compelling practical reasons that support the existence of a proprietary right — indeed, practical considerations militate against it."
Justice Edwards-Stuart added it was "quite impractical and unrealistic" to determine that ownership of the content of emails either belongs exclusively to the creator or the recipient of an email.