Skynet/misc_nixos-mailserver
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postfix: refactor and prune TLS settings

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- Groups settings between server and client
- Uses a range comparator for supported TLS versions
- Prune excluded primitives to what affects the supported TLS versions
This commit is contained in:
Martin Weinelt 2025-06-13 01:42:48 +02:00
parent e0ab4eeb67
commit e27326d317
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GPG key ID: 87C1E9888F856759
1 changed files with 28 additions and 22 deletions
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50
mail-server/postfix.nix
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@ -240,11 +240,6 @@ in
# Avoid leakage of X-Original-To, X-Delivered-To headers between recipients
lmtp_destination_recipient_limit = "1";
# Opportunistic DANE support
# https://www.postfix.org/postconf.5.html#smtp_tls_security_level
smtp_dns_support_level = "dnssec";
smtp_tls_security_level = "dane";
# sasl with dovecot
smtpd_sasl_type = "dovecot";
smtpd_sasl_path = "/run/dovecot2/auth";
@ -266,33 +261,44 @@ in
"check_policy_service unix:/run/dovecot2/quota-status"
];
# TLS settings, inspired by https://github.com/jeaye/nix-files
# Submission by mail clients is handled in submissionOptions
# TLS for incoming mail is optional
smtpd_tls_security_level = "may";
# Disable obselete protocols
smtpd_tls_protocols = "TLSv1.3, TLSv1.2, !TLSv1.1, !TLSv1, !SSLv2, !SSLv3";
smtp_tls_protocols = "TLSv1.3, TLSv1.2, !TLSv1.1, !TLSv1, !SSLv2, !SSLv3";
smtpd_tls_mandatory_protocols = "TLSv1.3, TLSv1.2, !TLSv1.1, !TLSv1, !SSLv2, !SSLv3";
smtp_tls_mandatory_protocols = "TLSv1.3, TLSv1.2, !TLSv1.1, !TLSv1, !SSLv2, !SSLv3";
# But required for authentication attempts
smtpd_tls_auth_only = true;
smtp_tls_ciphers = "high";
# TLS versions supported for the SMTP server
smtpd_tls_protocols = ">=TLSv1.2";
smtpd_tls_mandatory_protocols = ">=TLSv1.2";
# Require ciphersuites that OpenSSL classifies as "High"
smtpd_tls_ciphers = "high";
smtp_tls_mandatory_ciphers = "high";
smtpd_tls_mandatory_ciphers = "high";
# Disable deprecated ciphers
smtpd_tls_mandatory_exclude_ciphers = "MD5, DES, ADH, RC4, PSD, SRP, 3DES, eNULL, aNULL";
smtpd_tls_exclude_ciphers = "MD5, DES, ADH, RC4, PSD, SRP, 3DES, eNULL, aNULL";
smtp_tls_mandatory_exclude_ciphers = "MD5, DES, ADH, RC4, PSD, SRP, 3DES, eNULL, aNULL";
smtp_tls_exclude_ciphers = "MD5, DES, ADH, RC4, PSD, SRP, 3DES, eNULL, aNULL";
# Exclude cipher suites with undesirable properties
smtpd_tls_exclude_ciphers = "eNULL, aNULL";
smtpd_tls_mandatory_exclude_ciphers = "eNULL, aNULL";
# Opportunistic DANE support when delivering mail to other servers
# https://www.postfix.org/postconf.5.html#smtp_tls_security_level
smtp_dns_support_level = "dnssec";
smtp_tls_security_level = "dane";
# TLS versions supported for the SMTP client
smtp_tls_protocols = ">=TLSv1.2";
smtp_tls_mandatory_protocols = ">=TLSv1.2";
# Require ciphersuites that OpenSSL classifies as "High"
smtp_tls_ciphers = "high";
smtp_tls_mandatory_ciphers = "high";
# Exclude ciphersuites with undesirable properties
smtp_tls_exclude_ciphers = "eNULL, aNULL";
smtp_tls_mandatory_exclude_ciphers = "eNULL, aNULL";
# As long as all cipher suites are considered safe, let the client use its preferred cipher
tls_preempt_cipherlist = false;
# Allowing AUTH on a non encrypted connection poses a security risk
smtpd_tls_auth_only = true;
# Log only a summary message on TLS handshake completion
smtp_tls_loglevel = "1";
smtpd_tls_loglevel = "1";