{"description": "Mail servers are used to send and receive email over the network.\nMail is a very common service, and Mail Transfer Agents (MTAs) are obvious\ntargets of network attack.\nEnsure that systems are not running MTAs unnecessarily,\nand configure needed MTAs as defensively as possible.\n<br /><br />\nVery few systems at any site should be configured to directly receive email over the\nnetwork. Users should instead use mail client programs to retrieve email\nfrom a central server that supports protocols such as IMAP or POP3.\nHowever, it is normal for most systems to be independently capable of sending email,\nfor instance so that cron jobs can report output to an administrator.\nMost MTAs, including Postfix, support a submission-only mode in which mail can be sent from\nthe local system to a central site MTA (or directly delivered to a local account),\nbut the system still cannot receive mail directly over a network.\n<br /><br />\nThe <tt>alternatives</tt> program in Ubuntu 22.04 permits selection of other mail server software\n(such as Sendmail), but Postfix is the default and is preferred.\nPostfix was coded with security in mind and can also be more effectively contained by\nSELinux as its modular design has resulted in separate processes performing specific actions.\nMore information is available on its website, \n    <a xmlns='http://www.w3.org/1999/xhtml' href='http://www.postfix.org'>http://www.postfix.org</a>.", "warnings": [], "requires": [], "conflicts": [], "values": {}, "groups": ["postfix_client", "postfix_harden_os"], "rules": ["has_nonlocal_mta", "package_mailx_installed", "package_postfix_installed", "package_s-nail_installed", "package_sendmail_removed", "service_postfix_enabled"], "platform": "system_with_kernel", "platforms": ["system_with_kernel"], "inherited_platforms": [], "cpe_platform_names": ["system_with_kernel"], "title": "Mail Server Software", "definition_location": "/aptdata/openscap/scap-security-guide/linux_os/guide/services/mail/group.yml"}