Note: The Organization Management and eDiscovery role groups together contain the right permission roles to allow a user to search, preview search results and delete. You can choose to separate out these permissions as desired:

Under Assigned roles, confirm the Preview role is assigned.

Click the eDiscovery Manager role group.

Under Members, confirm the user you want to use is listed.

Under Assigned roles, confirm the Compliance Search and 'Search and Purge' roles are assigned.

Click the Organization Management role group.

Click Admin Centers, Security & Compliance.

Step 1: Check user has sufficient permissions to perform a content search, preview search results and delete messages If there are more than 10 items to be deleted per mailbox then either run multiple content search and deletes, or consider using Exchange PowerShell only to search and delete messages. This alternative method needs careful consideration as there is an increased risk of deleting messages you don't intend to. More detailed information on using Exchange PowerShell to search and delete is available from here.

This method will delete a maximum of 10 items per mailbox, from a total of 50,000 mailboxes. Step 3 - Use Security & Compliance Center PowerShell to delete the affected messages returned by the content search.Step 2 - Use the Security & Compliance Admin Center to create a content search to find affected messages.Step 1 - Check user has sufficient permissions to search, preview search results and delete messages.

The simplest way to find and remove messages uses three steps:

One or more users have received spam, phishing or other undesired emails. As an administrator you want to delete the emails from one or more user mailboxes. Provides steps to delete mailbox content from one or more mailboxes in Microsoft 365. How to delete an email from one or more mailboxes in Microsoft 365

Delete office 365 account