EHA Overview

The Microsoft Exchange Hosted Archive (EHA) service is an advanced message archiving and compliance system for email messages. Unlike traditional archiving methods that require hardware, software, and an IT staff to manage the system, EHA delivers message archiving as a service, without the additional hardware and software expenses. Because EHA is a service-based solution, it transfers the burden of application support to Microsoft rather than to your IT staff, which can result in lower costs to your organization and better use of your IT resources.

EHA can intercept and copy inbound, outbound, and internal email messages. All copies are then stored in a secure archive. With comprehensive message indexing, you can search stored messages by date, sender, recipients, header, subject line, contents, and attachment name. EHA storage can be used for retention periods of up to 10 years.

Note:
Office 365 for midsize businesses and enterprises provides information about message archiving in Office 365.