Confluence can archive and search emails - which is useful for tracking information over a long period of time and referencing emails in documents.
Benefits
Email archiving allows you to:
1) Keep a history of interaction typical locked in someone's inbox
2) Track an email thread
3) Search email contents
All of the email capture into Confluence is full-text searchable (including standard attachments).
4) Refer and link to email content from other Confluence content
Example
This link will show you an example of mail held in Confluence.