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<h4 class="subsection">3.13.1 Login delay</h4>

<p>POP3 clients often login frequently to check for new mail.  Each new
connection implies authenticating the user and opening his maildrop
and can be very resource consuming.  To reduce server load, it is
possible to impose a minimum delay between any two consecutive logins.
This is called &lsquo;<samp>LOGIN-DELAY</samp>&rsquo; capability and is described in RFC
2449.
</p>
<p>As of version 2.99.98, GNU Mailutils <code>pop3d</code> allows
to set global login delay, i.e. such enforcement will affect all POP3
users.  If a user attempts to log in before the specified login delay
expires, he will get the following error message:
</p>
<div class="example">
<pre class="example">-ERR [LOGIN-DELAY] Attempt to log in within the minimum login delay interval
</pre></div>

<p>The message will be issued after a valid password is entered.  This prevents
this feature from being used by malicious clients for account
harvesting.
</p>
<p>To enable the login delay capability, specify the minimum delay
using <code>login-delay</code> configuration statement, e.g.:
</p>
<div class="example">
<pre class="example">login-delay 60;
</pre></div>

<p>The <code>pop3d</code> utility keeps each user&rsquo;s last login time in a
special DBM file, called <em>login statistics database</em>, so to be
able to use this feature, Mailutils must be compiled with DBM support.
By default, the login statistics database is called
<samp>/var/run/pop3-login.db</samp>.  You can change its name using
<code>stat-file</code> configuration statement:
</p>
<div class="example">
<pre class="example">login-delay 60;
stat-file /tmp/pop.login.db;
</pre></div>

<p>The login delay facility will be enabled only if <code>pop3d</code> is
able to access the statistics database for both reading and
writing.  If it is not, it will report this using <code>syslog</code> and
start up without login delay restrictions.  A common error message
looks like:
</p>
<div class="example">
<pre class="example">Unable to open statistics db: Operation not permitted
</pre></div>

<p>You can check whether your <code>pop3d</code> uses login delays by
connecting to it and issuing the &lsquo;<samp>CAPA</samp>&rsquo; command.  If login delays
are in use, there response will contain the string &lsquo;<samp>LOGIN-DELAY
<var>n</var></samp>&rsquo;, where <var>n</var> is the actual login delay value.
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