TOSS 5 must be configured to prevent unrestricted mail relaying.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-282681 | TOSS-05-000207 | SV-282681r1201023_rule | CCI-000366 | medium |
| Description | ||||
| If unrestricted mail relaying is permitted, unauthorized senders could use this host as a mail relay for the purpose of sending spam or other unauthorized activity. | ||||
| STIG | Date | |||
| Tri-Lab Operating System Stack (TOSS) 5 Security Technical Implementation Guide | 2026-04-01 | |||
Details
Check Text (C-282681r1201023_chk)
Verify TOSS 5 is configured to prevent unrestricted mail relaying using the following command:
$ postconf -n smtpd_client_restrictions
smtpd_client_restrictions = permit_mynetworks,reject
If the "smtpd_client_restrictions" parameter contains any entries other than "permit_mynetworks" and "reject", and the additional entries have not been documented with the information system security officer (ISSO), this is a finding.
Fix Text (F-87147r1201022_fix)
Modify the postfix configuration file to restrict client connections to the local network using the following command:
$ sudo postconf -e 'smtpd_client_restrictions = permit_mynetworks,reject'