Email Manager offers several advantages over the standard SharePoint / Teams preview:
- performance. Email Manager typically shows an email in 1 s whereas it may take several seconds using the standard viewer
- view attachments. Email Manager allows users to view email attachments (Office, pdf, jpg, ...) directly in the browser
- extract email metadata during uploading. This requires a one-off configuration and zero involvement from end-users.
- tagging emails. Emails of interest can be tagged for future processing (move to other location, add metadata, ...) during viewing
- Email Manager shows sent and received dates in the local time zone (unlike the standard preview which uses UTC).
- optimised for handling large number of emails by offering previous/next buttons and the option to jump to a specific email
- can handle emails that are not rendered by the standard SharePoint viewers
- attach SharePoint / Teams document(s) to a new email
Email Manager's speed to display has the drawback that it does not always render complex emails (e.g. with tables, fancy B2C emails, ...) in their original lay-out.