About This Hotfix
An issue has been identified in the 8.8.0 release, published on 21st September 2023, that can cause client-initiated email sending to fail with an error, on installations with Microsoft as the Mail Provider and the OAuth authentication method.
For more information on symptoms, see https://help.whmcs.com/m/v88/l/1734321-email-sending-failed-call-to-undefined-function-whmcs-module-logadminactivity