Here are some guidelines in planning, implementing, and maintaining secure electronic mail systems for suitable to execute in most of the organization:
? Carefully plan and address the security aspects of the deployment of a mail server.
Careful planning is critical to the efficient implementation of a secure mail server. It is more difficult and costly to address security issues once the mail server is deployed. With careful planning, organizations can make sure that their mail servers meet their security requirements and are in compliance with all relevant organizational policies prior to installation, configuration, and deployment. Management controls are especially important in organizations where the information technology support structure is highly fragmented. This fragmentation can lead to inconsistencies in managing systems, and these inconsistencies often result in security vulnerabilities.
Organizations are more likely to make decisions about configuring computers appropriately and consistently when they develop and use a detailed, well-designed deployment plan. The development of such a plan will support mail server administrators in making the inevitable trade-off decisions between usability, performance, and risk.
Some of the issues that should be addressed in the organization’s deployment plan include:
* Purpose of the server and the services to be provided;
* Software to be installed;
* Users and their privileges;
* Security and privacy issues;
* Management practices and procedures to assure secure systems;
* Types of personnel required for deployment and operational phases of the mail server and the supporting infrastructure. Personnel types that should be considered include system and mail server administrators, network administrators, and information systems security officers;
* Skills and training required by assigned personnel; and
* Availability of personnel.
? Implement appropriate security management practices and controls when maintaining and operating a secure mail server.
Appropriate management practices are essential to operating and maintaining a secure mail server. As part of their comprehensive planning and management practices, organizations should identify their systems and information to be protected, and then develop, document, and implement the policies, standards, procedures, and guidelines that will help to ensure the confidentiality, integrity, and availability of information system resources.
To ensure the security of a mail server and the supporting network infrastructure, the following practices should be implemented:
* Organization-wide information system security policy;
* Configuration/change control and management;
* Risk assessment and management;
* Standardized software configurations that satisfy the information system security policy;
* Security awareness and training;
* Contingency, continuity of operations, and disaster recovery planning; and
* Certification and accreditation.
? Ensure that the mail server operating system is deployed, configured, and managed to meet the security requirements of the organization.
The first step in securing a mail server is to secure the underlying operating system. Most commonly available mail servers operate on a general-purpose operating system. Many security issues can be avoided if the operating system’s underlying mail servers are configured appropriately. Default hardware and software configurations are typically set by manufacturers to emphasize features, functions, and ease of use at the expense of security. Because manufacturers are not aware of each organization’s security needs, each mail server administrator must configure new servers to reflect their organization’s security requirements and reconfigure them as those requirements change. Using security configuration guides or checklists can assist administrators in securing systems consistently and efficiently. To secure the operating system, organizations should carry out the following steps:
* Patch and update the operating system;
* Remove or disable unnecessary services and applications;
* Configure operating system user authentication;
* Configure resource controls;
* Install and configure additional security controls if needed; and
* Perform security tests on the operating system.
? Ensure that the mail server application is deployed, configured, and managed to meet the security requirements of the organization.
Many of the steps outlined for the security of the operating system apply also to the secure installation and configuration of the mail server application. The basic recommendation is that organizations install the minimal mail server services required and eliminate any known vulnerabilities through patches or upgrades. If an installation program installs unnecessary applications, services, or scripts, they should be removed immediately after the installation process has been completed. The following steps should be performed in securing the mail server application:
* Patch and upgrade the mail server application;
* Remove or disable unnecessary services, applications, and sample content;
* Configure mail server user authentication and access controls;
* Configure mail server resource controls; and
* Test the security of the mail server applications.
? Consider the implementation of cryptographic technologies to protect user authentication and mail data.
Most standard mail protocols default to unencrypted user authentication and send email data unencrypted through the network. When unprotected data is sent, an attacker may be able to easily compromise a user account and to intercept or alter unencrypted email messages. Most organizations should consider encrypting the user authentication session even if they do not encrypt the email data itself. Encrypted user authentication is now supported by most standard and proprietary mailbox protocols.
Organizations should examine closely the decision about whether to encrypt and sign email data. Encrypting and signing email places a greater load on the user’s computer and the organization’s network infrastructure, and this practice may complicate malware scanning and email content filtering. Encrypting and signing messages may also result in significant administrative overhead and may increase the costs of managing email systems. However, for many organizations, the benefits of email encryption and signatures will outweigh the costs.
? Employ the network infrastructure to protect mail servers.
The network infrastructure includes the firewalls, routers, and the intrusion detection and prevention systems that support the mail server. These systems play a critical role in the security of the mail server. In most configurations, the network infrastructure will be the first line of defense between the Internet and a mail server. Network design alone, however, cannot protect a mail server. Because of the frequency, sophistication, and variety of mail server attacks that occur today, organizations should consider protecting their mail servers through layered and diverse protection mechanisms.
? Ensure that the mail clients are deployed, configured, and used properly to meet the security requirements of the organization.
The client side of the electronic mail process may represent a greater risk to the security of the mail system than the mail server functions. Organizations must address numerous issues in order to provide an appropriate level of security for email clients. The following steps will help organizations with the secure installation, configuration, and implementation of mail client applications:
* Patch and upgrade the mail client applications;
* Configure mail client security features, such as disabling automatic opening of messages and enabling antispam and anti-phishing features;
* Configure mailbox authentication and access; and
* Secure the client host’s operating system.
? Maintain the security of a mail server as an ongoing process.
Organizations should devote constant effort, resources, and vigilance to maintain a secure mail server. The mail server should be monitored and maintained on a daily basis to assure mail security. To maintain the security of a mail server, organizations should take the following actions:
* Configure, protect, and analyze log files;
* Back up data frequently;
* Protect against malware (e.g., viruses, worms, Trojan horses);
* Establish and implement procedures for recovering from compromise;
* Test and apply patches in a timely manner; and
* Test the security of the system periodically.
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