Zimbra - Zimbra is trusted by over 500 million users to increase productivity with a complete set of collaboration tools while maintaining total control over security and privacy.
Dext - Receipt Bank converts key information from your bills, receipts and invoices into data you and your company can use! No obligation Free Trial available.
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
DOKKA.com - The Future has Arrived: Accounting Process Automation
mailcow - An open source mailserver suite.
EntryRocket - Simplify your bookkeeping by automating file imports into Xero.