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Replacements for Deprecated Features

多肉大叔
April 22, 2025

Excerpted from the Postfix Replacements for Deprecated Features on April 22, 2025.

Purpose of this document

This document describes Postfix features that are deprecated (will be removed) or that have already been removed. It also has tips for making an existing Postfix configuration more future-proof.

Overview:

Why deprecate? 

Sometimes, a Postfix feature needs to be replaced with a different one. To give an example:

  • The initial Postfix TLS implementation used multiple boolean parameters: one parameter to enable opportunistic TLS (for example, "smtp_enforce_tls = yes") and one parameter to enable mandatory TLS (for example, "smtp_require_tls = yes").
  • As we added support more features such as fingerprint, dane, and so on, we decided not to add more boolean parameters. Instead we introduced one configuration parameter to select from multiple deployment models (for example, smtp_tls_security_level = may | encrypt | dane, etc...).

Having both the "old" and "new" way to configure Postfix is convenient for existing Postfix installations, because their configuration does not break after an upgrade to a new version. Unfortunately, there are also disadvantages. Having multiple ways to do similar things is not only confusing for newcomers, it also makes Postfix harder to change.

Deprecation process 

The basic process steps are:

  1. Inform humans that a feature will be removed, and suggest replacements, in logging and documentation.
  2. Remove the feature, and update logging and documentation.

Disclaimer: it has taken 20 years for some features to be removed. This past is not a guarantee for the future.

Deprecated features 

The table summarizes removed or deprecated features and replacements. Click on the "obsolete feature" name for a more detailed description.

Obsolete feature nameWarning as 
of version		Removed 
in version		Replacement
disable_dns_lookups 3.9-smtp_dns_support_level
xxx_use_tls 3.9-xxx_tls_security_level
xxx_enforce_tls 3.9-xxx_tls_security_level
xxx_per_site 3.9-xxx_policy_maps
smtpd_tls_dh1024_param_file 3.9-do not specify (leave at default)
smtpd_tls_eecdh_grade 3.9-do not specify (leave at default)
permit_mx_backup 3.9-relay_domains
check_relay_domains 2.23.9permit_mynetworks, reject_unauth_destination
reject_maps_rbl 2.13.9reject_rbl_client
permit_naked_ip_address 2.03.9permit_mynetworks, permit_sasl_authenticated

Obsolete DNS on/off configuration 

The postconf(1) command logs the following:

Replace obsolete configuration with its replacement:

GoalObsolete configurationReplacement configuration
To disable DNS lookups in the Postfix SMTP/LMTP clientdisable_dns_lookups = yessmtp_dns_support_level = disabled
To enable DNS lookups in the Postfix SMTP/LMTP clientdisable_dns_lookups = noLeave smtp_dns_support_level at the implicit default which is empty, unless you need a higher support level such as DNSSEC.

Obsolete opportunistic TLS configuration 

The postconf(1) command logs one of the following:

There are similarly-named parameters and warnings for postscreen(8) and tlsproxy(8), but those parameters should rarely be specified by hand.

Replace obsolete configuration with its replacement:

GoalObsolete configurationReplacement configuration
To turn off TLSxxx_use_tls = noxxx_security_level = none
To turn on opportunistic TLSxxx_use_tls = yesxxx_security_level = may

Obsolete mandatory TLS configuration 

The postconf(1) command logs one of the following:

There are similarly-named parameters and warnings for postscreen(8) and tlsproxy(8), but those parameters should rarely be specified by hand.

Replace obsolete configuration with its replacement:

GoalObsolete configurationReplacement configuration
To turn off mandatory TLSxxx_enforce_tls = noxxx_security_level = may
To turn on mandatory TLSxxx_enforce_tls = yesxxx_security_level = encrypt

Obsolete TLS policy table configuration 

The postconf(1) command logs one of the following:

There is similarly-named parameter and warning for tlsproxy(8), but that parameter should rarely be specified by hand.

Unfortunately, this is more than a name change: the table format has changed too, as has the table search process. There is no simple conversion of the obsolete form to its replacement.

check_relay_domains 

Depending on the Postfix version, the Postfix SMTP daemon logs following warning:

This feature was removed because it would relay based on the client domain name, which is not robust.

Recommended configuration to prevent an "open relay" problem with the SMTP service on port 25:

main.cf:
    smtpd_recipient_restrictions = 
        permit_mynetworks, 
        permit_sasl_authenticated, 
        reject_unauth_destination
        ...other restrictions...

Or equivalent in smtpd_relay_restrictions.

permit_mx_backup

The Postfix version 3.9 and later SMTP daemon logs the following warning:

This feature will be removed because it is too difficult to configure recipient address validation, making Postfix a source of backscatter bounces.

To specify the domains that Postfix will provide MX backup service for, see Configuring Postfix as primary or backup MX host for a remote site.

reject_maps_rbl

Depending on the Postfix version, the SMTP daemon logs one of the following warnings:

  • support for restriction "reject_maps_rbl" has been removed in Postfix 3.9"; instead, specify "reject_rbl_client domain-name"
  • support for restriction "reject_maps_rbl" will be removed from Postfix; use "reject_rbl_client domain-name" instead

This feature was replaced because "MAPS RBL" is the name of a specific reputation service. The reject_rbl_client feature provides a superset of the reject_maps_rbl functionality.

Recommended configuration:

main.cf:
    smtpd_recipient_restrictions =
        permit_mynetworks,
        permit_sasl_authenticated,
        reject_unauth_destination
        reject_rbl_client domain-name
        ...other restrictions...

Where domain-name is the domain name of a DNS reputation service.

permit_naked_ip_address

Depending on the Postfix version, the SMTP daemon logs one of the following warnings:

This feature was removed because it was easy to get a false match when smtpd_recipient_restrictions was intended to match a remote SMTP client IP address.

Recommended configuration:

main.cf:
    smtpd_recipient_restrictions =
        permit_mynetworks,
        permit_sasl_authenticated,
        reject_unauth_destination
        reject_rbl_client domain-name
        ...other restrictions...

That is, no restriction on HELO or EHLO syntax. Such restrictions ar rarely useful nowadays.