in-place eDiscovery & hold

Hi experts we are using exchange hybrid environment,

i want to export one of my onpremise users 2016 emails, when i do in-place eDiscovery & hold, i am getting below error An unknown error occurred on the search server. Please contact your administrator for assistance. The message from the search server is 'To execute a mailbox search, the user needs to have a SMTP email address.'. experts help me to troubleshoot this issue