---
title: Choosing a Web Server for your HMS Installation
description: As of version 2.1, the Hurricane MTA Server (HMS) now comes with two options for running its component web applications such as the MTA Control Panel or Open and Click Tracking. The two options are Ca
---
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# Choosing a Web Server for your HMS Installation
As of version 4.0, Hurricane MTA Server (HMS) now works exclusively with Microsoft IIS web server. The installer will install all prerequisites necessary to run on server 2018 versions and later.
> ### Applies to HMS Version: 2.1 - 3.0
>
> As of version 2.1, the Hurricane MTA Server (HMS) now comes with two options for running its component web applications such as the MTA Control Panel or Open and Click Tracking. The two options are Cassini, an embedded web server, and IIS, the fully featured web server built into all versions of Windows Server.
>
> #### Cassini
>
> Before version 2.1, Cassini was the only web server option. This option continues to be available, and should be selected instead of IIS in the following scenarios:
>
> - IIS cannot be used due to security requirements or concerns
> - Wanting to avoid optional configuration changes to an existing HMS instance
> - Wanting to avoid having a fully featured web server running on the MTA's server
>
> #### Internet Information Services (IIS)
>
> IIS is a more feature-rich web server and also operates external to the HMS. Some of the benefits of using IIS are:
>
> - Significant speed improvement over Cassini
> - Ability to fully customize web application settings through the IIS Manager utility, installed alongside IIS
> - Additional security features provided by an enterprise web server, such as SSL support
Be aware that while IIS makes advanced web server configuration possible, the IIS Manager utility must be used to configure IIS. We recommend having some knowledge of the IIS Manager utility before using it to make configuration changes. Information about how to use this tool is widely available online, and a good place to start would be an article such as: Getting Started with IIS Manager in IIS 7 and IIS 8.
### Security Concerns
It should be noted that using IIS also performs the following actions on the system, which may or may not be acceptable based on your security policy:
- Creation of four Application Pools within IIS' configuration
- Creation of four Sites within IIS' configuration
- Creation of multiple Windows OS users and groups on the system, including:
- 'IIS\_IUSRS' Group, created by default by IIS
- Four "IIS AppPool" users, one for each Pool+Site installed with the MTA. Each user has permissions for either group 'Administrators' or group 'Performance Monitor Users' depending on their needs
### Switching Between Web Servers
Switching back and forth between web servers is easily accomplished by simply rerunning the MTA installer and selecting a different option. Using the installer to switch back and forth is required as port bindings and similar configurations are cleaned up from the previous option by our installation process, avoiding any conflicts. When switching between web servers we do not erase any existing configurations, so even custom IIS configurations will be preserved if an MTA is switched from IIS to using Cassini and back to IIS again. If you wish to revert to the default IIS site configurations, please manually remove the appropriate Sites and Application Domains via the IIS Manager utility before reinstalling the MTA.
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