diff --git a/en_US/upgrade/0-upgrade.iredmail.0.9.9-1.0.md b/en_US/upgrade/0-upgrade.iredmail.0.9.9-1.0.md
index 5acb06f7..1f934fff 100644
--- a/en_US/upgrade/0-upgrade.iredmail.0.9.9-1.0.md
+++ b/en_US/upgrade/0-upgrade.iredmail.0.9.9-1.0.md
@@ -2,6 +2,10 @@
 
 [TOC]
 
+!!! warning
+
+    This is still a __DRAFT__ document, do __NOT__ apply it.
+
 !!! note "Paid Remote Upgrade Support"
 
     We offer remote upgrade support if you don't want to get your hands dirty,
@@ -72,3 +76,21 @@ latest stable release immediately:
 ### Upgrade netdata to the latest stable release (1.12.1)
 
 If you have netdata installed, you can upgrade it by following this tutorial: [Upgrade netdata](./upgrade.netdata.html).
+
+### Fail2ban: slightly loose filter rule for postfix
+
+We received few reports from clients that Outlook for macOS may trigger some
+unexpected smtp errors, and caught by the Fail2ban filter rules shipped by
+iRedMail, so we decide to remove the filter rule used to match Postfix log
+`lost connection after EHLO`.
+
+Please follow commands below to get the updated filter rules.
+
+* On Linux:
+
+```
+cd /etc/fail2ban/filter.d/
+wget -O postfix.iredmail.conf https://bitbucket.org/zhb/iredmail/raw/default/iRedMail/samples/fail2ban/filter.d/postfix.iredmail.conf
+```
+
+Restarting Fail2ban service is required.
diff --git a/html/upgrade.iredmail.0.9.9-1.0.html b/html/upgrade.iredmail.0.9.9-1.0.html
index 6ca1d238..b4f4b7df 100644
--- a/html/upgrade.iredmail.0.9.9-1.0.html
+++ b/html/upgrade.iredmail.0.9.9-1.0.html
@@ -27,12 +27,17 @@
 <li><a href="#upgrade-mlmmjadmin-to-the-latest-stable-release-21">Upgrade mlmmjadmin to the latest stable release (2.1)</a></li>
 <li><a href="#upgrade-roundcube-webmail-to-the-latest-stable-release">Upgrade Roundcube webmail to the latest stable release</a></li>
 <li><a href="#upgrade-netdata-to-the-latest-stable-release-1121">Upgrade netdata to the latest stable release (1.12.1)</a></li>
+<li><a href="#fail2ban-slightly-loose-filter-rule-for-postfix">Fail2ban: slightly loose filter rule for postfix</a></li>
 </ul>
 </li>
 </ul>
 </li>
 </ul>
 </div>
+<div class="admonition warning">
+<p class="admonition-title">Warning</p>
+<p>This is still a <strong>DRAFT</strong> document, do <strong>NOT</strong> apply it.</p>
+</div>
 <div class="admonition note">
 <p class="admonition-title">Paid Remote Upgrade Support</p>
 <p>We offer remote upgrade support if you don't want to get your hands dirty,
@@ -89,7 +94,21 @@ latest stable release immediately:</p>
 <li><a href="https://github.com/roundcube/roundcubemail/wiki/Upgrade">How to upgrade Roundcube</a>.</li>
 </ul>
 <h3 id="upgrade-netdata-to-the-latest-stable-release-1121">Upgrade netdata to the latest stable release (1.12.1)</h3>
-<p>If you have netdata installed, you can upgrade it by following this tutorial: <a href="./upgrade.netdata.html">Upgrade netdata</a>.</p><div class="footer">
+<p>If you have netdata installed, you can upgrade it by following this tutorial: <a href="./upgrade.netdata.html">Upgrade netdata</a>.</p>
+<h3 id="fail2ban-slightly-loose-filter-rule-for-postfix">Fail2ban: slightly loose filter rule for postfix</h3>
+<p>We received few reports from clients that Outlook for macOS may trigger some
+unexpected smtp errors, and caught by the Fail2ban filter rules shipped by
+iRedMail, so we decide to remove the filter rule used to match Postfix log
+<code>lost connection after EHLO</code>.</p>
+<p>Please follow commands below to get the updated filter rules.</p>
+<ul>
+<li>On Linux:</li>
+</ul>
+<pre><code>cd /etc/fail2ban/filter.d/
+wget -O postfix.iredmail.conf https://bitbucket.org/zhb/iredmail/raw/default/iRedMail/samples/fail2ban/filter.d/postfix.iredmail.conf
+</code></pre>
+
+<p>Restarting Fail2ban service is required.</p><div class="footer">
     <p style="text-align: center; color: grey;">All documents are available in <a href="https://bitbucket.org/zhb/iredmail-docs/src">BitBucket repository</a>, and published under <a href="http://creativecommons.org/licenses/by-nd/3.0/us/" target="_blank">Creative Commons</a> license. You can <a href="https://bitbucket.org/zhb/iredmail-docs/get/tip.tar.bz2">download the latest version</a> for offline reading. If you found something wrong, please do <a href="https://www.iredmail.org/contact.html">contact us</a> to fix it.</p>
 </div>
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