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<h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix
Backwards-Compatibility Safety Net</h1>
<hr>
<h2>Purpose of this document </h2>
<p> Postfix 3.0 introduces a safety net that runs Postfix programs
with backwards-compatible default settings after an upgrade. The
safety net will log a warning whenever a "new" default setting could
have an negative effect on your mail flow. </p>
<p>This document provides information on the following topics: </p>
<ul>
<li> <p> <a href="#overview">Detailed descriptions</a> of Postfix
backwards-compatibility warnings.
<li> <p> What backwards-compatible settings you may have to make
permanent in main.cf or master.cf. </p>
<li> <p> <a href="#turnoff">How to turn off</a> Postfix
backwards-compatibility warnings. </p>
</ul>
<h2> <a name="overview"> Overview </a> </h2>
<p> With backwards compatibility turned on, Postfix logs a message
whenever a backwards-compatible default setting may be required for
continuity of service. Based on this logging the system administrator
can decide if any backwards-compatible settings need to be made
permanent in main.cf or master.cf, before <a href="#turnoff">turning
off the backwards-compatibility safety net</a> as described at the
end of this document. </p>
<p> The following messages may be logged: </p>
<ul>
<li> <p> <a href="#append_dot_mydomain"> Using backwards-compatible
default setting append_dot_mydomain=yes </a> </p>
<li> <p> <a href="#chroot"> Using backwards-compatible default setting
chroot=y</a> </p>
<li> <p> <a href="#mynetworks_style"> Using backwards-compatible
default setting mynetworks_style=subnet </a> </p>
<li> <p> <a href="#relay_domains"> Using backwards-compatible default
setting relay_domains=$mydestination </a> </p>
<li> <p> <a href="#smtputf8_enable"> Using backwards-compatible
default setting smtputf8_enable=no</a> </p>
</ul>
<p> If such a message is logged in the context of a legitimate
request, the system administrator should make the backwards-compatible
setting permanent in main.cf or master.cf, as detailed in the
sections that follow. </p>
<p> When no more backwards-compatible settings need to be made
permanent, the system administrator should <a href="#turnoff">turn
off the backwards-compatibility safety net</a> as described at the
end of this document. </p>
<h2> <a name="append_dot_mydomain"> Using backwards-compatible default
setting append_dot_mydomain=yes</a> </h2>
<p> The append_dot_mydomain default value has changed from "yes"
to "no". As long as the append_dot_mydomain parameter is left at
its implicit default value, and the backwards-compatible default
setting is turned on, Postfix may log one of the following messages:</p>
<ul>
<li> <p> Messages about missing "localhost" in mydestination or
other address class: </p>
<blockquote>
<pre>
postfix/trivial-rewrite[14777]: using backwards-compatible
default setting append_dot_mydomain=yes to rewrite
"localhost" to "localhost.example.com"; please add
"localhost" to mydestination or other address class
</pre>
</blockquote>
<p> If Postfix logs the above message, add "localhost" to
mydestination (or virtual_alias_domains, virtual_mailbox_domains,
or relay_domains) and execute the command "<b>postfix reload</b>".
<li> <p> Messages about incomplete domains in email addresses: </p>
<blockquote>
<pre>
postfix/trivial-rewrite[25835]: using backwards-compatible
default setting append_dot_mydomain=yes to rewrite "foo" to
"foo.example.com"
</pre>
</blockquote>
<p> If Postfix logs the above message for domains different from
"localhost", and the sender cannot be changed to use complete domain
names in email addresses, then the system administrator should make
the backwards-compatible setting "append_dot_mydomain = yes" permanent
in main.cf: </p>
<blockquote>
<pre>
# <b>postconf append_dot_mydomain=yes</b>
# <b>postfix reload</b>
</pre>
</blockquote>
</ul>
<h2> <a name="chroot"> Using backwards-compatible default
setting chroot=y</a> </h2>
<p> The master.cf chroot default value has changed from "y" (yes)
to "n" (no). As long as a master.cf chroot field is left at its
implicit default value, and the backwards-compatible default setting
is turned on, Postfix may log the following message while it
reads the master.cf file: </p>
<blockquote>
<pre>
postfix/master[27664]: /etc/postfix/master.cf: line 72: using
backwards-compatible default setting chroot=y
</pre>
</blockquote>
<p> If this service should remain chrooted, then the system
administrator should make the backwards-compatible setting "chroot
= y" permanent in master.cf. For example, to update the chroot
setting for the "smtp inet" service: </p>
<blockquote>
<pre>
# <b>postconf -F smtp/inet/chroot=y</b>
# <b>postfix reload</b>
</pre>
</blockquote>
<h2> <a name="mynetworks_style"> Using backwards-compatible default
setting mynetworks_style=subnet</a> </h2>
<p> The mynetworks_style default value has changed from "subnet"
to "host". This parameter is used to implement the "permit_mynetworks"
feature. As long as the mynetworks and mynetworks_style parameters
are left at their implicit default values, and the backwards-compatible
default setting is turned on, the Postfix SMTP server may log one
of the following messages: </p>
<blockquote>
<pre>
postfix/smtpd[17375]: using backwards-compatible default setting
mynetworks_style=subnet to permit request from client
"foo.example.com[10.1.1.1]"
</pre>
</blockquote>
<blockquote>
<pre>
postfix/postscreen[24982]: using backwards-compatible default
setting mynetworks_style=subnet to permit request from client
"10.1.1.1"
</pre>
</blockquote>
<p> If the client request should not be rejected, then the system
administrator should make the backwards-compatible setting
"mynetworks_style = subnet" permanent in main.cf: </p>
<blockquote>
<pre>
# <b>postconf mynetworks_style=subnet</b>
# <b>postfix reload</b>
</pre>
</blockquote>
<h2><a name="relay_domains"> Using backwards-compatible default
setting relay_domains=$mydestination </a> </h2>
<p> The relay_domains default value has changed from "$mydestination"
to the empty value. As long as the relay_domains parameter is left
at its implicit default value, and the backwards-compatible default
setting is turned on, Postfix may log one of the following messages.
</p>
<ul>
<li> <p> Messages about accepting mail for a remote domain:</p>
<blockquote>
<pre>
postfix/smtpd[19052]: using backwards-compatible default setting
relay_domains=$mydestination to accept mail for domain
"foo.example.com"
</pre>
</blockquote>
<blockquote>
<pre>
postfix/smtpd[19052]: using backwards-compatible default setting
relay_domains=$mydestination to accept mail for address
"user@foo.example.com"
</pre>
</blockquote>
<li> <p> Messages about providing ETRN service for a remote domain:</p>
<blockquote>
<pre>
postfix/smtpd[19138]: using backwards-compatible default setting
relay_domains=$mydestination to flush mail for domain
"bar.example.com"
</pre>
</blockquote>
<blockquote>
<pre>
postfix/smtp[13945]: using backwards-compatible default setting
relay_domains=$mydestination to update fast-flush logfile for
domain "bar.example.com"
</pre>
</blockquote>
</ul>
<p> If Postfix should continue to accept mail for that domain or
continue to provide ETRN service for that domain, then the system
administrator should make the backwards-compatible setting
"relay_domains = $mydestination" permanent in main.cf: </p>
<blockquote>
<pre>
# <b>postconf 'relay_domains=$mydestination'</b>
# <b>postfix reload</b>
</pre>
</blockquote>
<p> Note: quotes are required as indicated above. </p>
<p> Instead of $mydestination, it may be better to specify an
explicit list of domain names. </p>
<h2> <a name="smtputf8_enable"> Using backwards-compatible default
setting smtputf8_enable=no</a> </h2>
<p> The smtputf8_enable default value has changed from "no" to "yes.
With the new "yes" setting, the Postfix SMTP server rejects non-ASCII
addresses from clients that don't request SMTPUTF8 support. With
the old "no" setting, Postfix will accept such addresses, even if
such addresses are not permitted by traditional SMTP standards. </p>
<p> As long as the smtputf8_enable parameter is left at its implicit
default value, and the backwards-compatible default setting is
turned on, Postfix logs a warning each time an SMTP command uses a
non-ASCII address localpart without requesting SMTPUTF8 support: </p>
<blockquote>
<pre>
postfix/smtpd[27560]: using backwards-compatible default setting
smtputf8_enable=no to accept non-ASCII sender address
"??@example.org" from localhost[127.0.0.1]
</pre>
</blockquote>
<blockquote>
<pre>
postfix/smtpd[27560]: using backwards-compatible default setting
smtputf8_enable=no to accept non-ASCII recipient address
"??@example.com" from localhost[127.0.0.1]
</pre>
</blockquote>
<p> If the address should not be rejected, and the client cannot
be updated to use SMTPUTF8, then the system administrator should
make the backwards-compatible setting "smtputf8_enable = no" permanent
in main.cf:
<blockquote>
<pre>
# <b>postconf smtputf8_enable=no</b>
# <b>postfix reload</b>
</pre>
</blockquote>
<h2> <a name="turnoff">Turning off the backwards-compatibility safety net</a> </h2>
<p> Backwards compatibility is turned off by updating the
compatibility_level setting in main.cf. </p>
<blockquote>
<pre>
# <b>postconf compatibility_level=<i>N</i></b>
# <b>postfix reload</b>
</pre>
</blockquote>
<p> For <i>N</i> specify the number that is logged in your postfix(1)
warning message: </p>
<blockquote>
<pre>
warning: To disable backwards compatibility use "postconf compatibility_level=<i>N</i>" and "postfix reload"
</pre>
</blockquote>
<p> Sites that don't care about backwards compatibility may set
"compatibility_level = 9999" at their own risk. </p>
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