"Installing an agent" means placing the script that handles events into the folder being monitored for events. As a developer, you do this when you first create the script and every time you edit it and save the changes.
Not just anybody can install an agent. For security purposes, Microsoft Exchange Server restricts this action to persons with an Exchange mailbox associated with a Windows NT® user account. The Exchange account (as identified within Microsoft Exchange Server by its e-mail alias) must also have been granted permissions on the monitored folder sufficient for saving files into it, in this case the agent.
Note This account must exist and have proper permissions before you start developing the agent (writing its script). Otherwise, you cannot save the agent into the monitored folder, which also means you cannot test it.
The actions performed by agents — creating, routing, and deleting messages and other documents — represent a good deal of power within the Microsoft Exchange Server installation. To help ensure that this power is not abused, an agent must operate within the security limits imposed by an administrator.
So that these limits are enforced, an agent must log on using an Outlook profile every time it runs. By default, this is the profile of the person who installed the agent. In this way, all of your agents acquire an exact copy of your Exchange permissions when running. However, if you leave the organization and your mailbox is disabled, all of your scripts will stop running, because they can no longer log on to Microsoft Exchange Server.
It is recommended that developers create a specific "agent" account to use for installing and running scripts.
To create a Microsoft Exchange Server user account
This procedure also creates a mailbox for the Event Service service account. This service account is used for installing Event Service scripts, which also run in the context of this account.
To find the name of the Microsoft Exchange Event Service service account