Retention of emails relating to general correspondence are usually held for 3 months. However, emails relating to the following legal purposes must be retained longer:
Contracts: 6 years
Defamation: 1 year
Leases: 12 years
Negligence (and other ‘Torts’): 6 years
Personal injury: 3 years
Rent: 6 years
Sums recoverable by statute: 6 years
To recover land: 12 years
Before submitting a FOI complaint to the ICO, have you requested an internal review concerning the missing information? The ICO expects requesters to submit an internal review before raising a complaint.
You may also find this ICO guidance helpful:
Fact sheet for councils: the use of personal email addresses and devices