You can export certain reports to Excel or CSV by clicking on Download in the top right hand corner of the report screen, and then selecting the format in which you would like to download the report.
The following reports can be exported into Excel or CSV:
Overview
Contacts
Trend
Teams
Shared / Group Mailboxes
Conversation Logs
Message Logs
NOTE: Exporting from the conversation log will only provide the first emails for each conversation. If you export from the messages log you will receive ALL email data.