piler is an open source email archival application.

Features:

- built-in smtp server

- clamd support

- archival rules

- retention rules

- legal hold

- message and attachment deduplication

- message compression

- message encryption

- digital fingerprinting and verification

- full text search

- simple and expert search

- save search criteria

- tagging emails

- view, export, restore emails

- bulk import/export messages

- access control

- AD / LDAP authentication

- IMAP, POP3 authentication

- single sign-on (SSO)

- Google Apps support

- Office 365 support

- STARTTLS support

- Google Authenticator support for 2-factor authentication

- i18n

- customisable theme

- audit logs

- search in audit logs

- online status info

- accounting

- recognised formats: PST, EML, Maildir, mailbox