diff --git a/en_US/installation/0-install.iredmail.on.debian.ubuntu.md b/en_US/installation/0-install.iredmail.on.debian.ubuntu.md
index b5b08dea..acc70742 100644
--- a/en_US/installation/0-install.iredmail.on.debian.ubuntu.md
+++ b/en_US/installation/0-install.iredmail.on.debian.ubuntu.md
@@ -19,6 +19,7 @@ To install iRedMail on Debian or Ubuntu Linux, you need:
   [Download](../download.html) page.
 * `2 GB` of memory is recommended for a low traffic production server.
   Spam/Virus scanning will take most system resource.
+* Make sure 3 UID/GID are not used by other user/group: 2000, 2001, 2002.
 
 Notes:
 
diff --git a/en_US/installation/0-install.iredmail.on.freebsd.md b/en_US/installation/0-install.iredmail.on.freebsd.md
index bc58924c..df82b644 100644
--- a/en_US/installation/0-install.iredmail.on.freebsd.md
+++ b/en_US/installation/0-install.iredmail.on.freebsd.md
@@ -24,6 +24,7 @@ To install iRedMail on FreeBSD, you need:
   [Download](../download.html) page.
 * `2 GB` of memory is recommended for a low traffic production server.
   Spam/Virus scanning will take most system resource.
+* Make sure 3 UID/GID are not used by other user/group: 2000, 2001, 2002.
 
 Note: All packages will be installed from ports tree.
 
diff --git a/en_US/installation/0-install.iredmail.on.freebsd.with.jail.md b/en_US/installation/0-install.iredmail.on.freebsd.with.jail.md
index cee8094b..85e2508b 100644
--- a/en_US/installation/0-install.iredmail.on.freebsd.with.jail.md
+++ b/en_US/installation/0-install.iredmail.on.freebsd.with.jail.md
@@ -28,6 +28,7 @@ and it may not be working as expected.
 
 * The latest stable release of iRedMail. You can download it here: http://www.iredmail.org/download.html
 * Port `sysutils/ezjail` for FreeBSD.
+* Make sure 3 UID/GID are not used by other user/group: 2000, 2001, 2002.
 
 ## Preparations
 
diff --git a/en_US/installation/0-install.iredmail.on.openbsd.md b/en_US/installation/0-install.iredmail.on.openbsd.md
index fb14f5e1..a88b5d8b 100644
--- a/en_US/installation/0-install.iredmail.on.openbsd.md
+++ b/en_US/installation/0-install.iredmail.on.openbsd.md
@@ -28,6 +28,8 @@ To install iRedMail on OpenBSD, you need:
     * man[XX].tgz
     * xbase[XX].tgz
 
+* Make sure 3 UID/GID are not used by other user/group: 2000, 2001, 2002.
+
 !!! note
 
     * All binary packages will be installed with command `pkg_add -i`. It will
diff --git a/en_US/installation/0-install.iredmail.on.rhel.md b/en_US/installation/0-install.iredmail.on.rhel.md
index 8f59652c..b1e51145 100644
--- a/en_US/installation/0-install.iredmail.on.rhel.md
+++ b/en_US/installation/0-install.iredmail.on.rhel.md
@@ -19,6 +19,7 @@ To install iRedMail on RHEL or CentOS Linux, you need:
   [Download](../download.html) page.
 * `2 GB` of memory is recommended for a low traffic production server.
   Spam/Virus scanning will take most system resource.
+* Make sure 3 UID/GID are not used by other user/group: 2000, 2001, 2002.
 
 ## Preparations
 
diff --git a/html/install.iredmail.on.debian.ubuntu.html b/html/install.iredmail.on.debian.ubuntu.html
index b24ebed8..12ea0631 100644
--- a/html/install.iredmail.on.debian.ubuntu.html
+++ b/html/install.iredmail.on.debian.ubuntu.html
@@ -55,6 +55,7 @@ modifying, and it may not be working as expected.</p>
   <a href="../download.html">Download</a> page.</li>
 <li><code>2 GB</code> of memory is recommended for a low traffic production server.
   Spam/Virus scanning will take most system resource.</li>
+<li>Make sure 3 UID/GID are not used by other user/group: 2000, 2001, 2002.</li>
 </ul>
 <p>Notes:</p>
 <ul>
diff --git a/html/install.iredmail.on.freebsd.html b/html/install.iredmail.on.freebsd.html
index ea8b1871..672283af 100644
--- a/html/install.iredmail.on.freebsd.html
+++ b/html/install.iredmail.on.freebsd.html
@@ -58,6 +58,7 @@ modifying, and it may not be working as expected.</p>
   <a href="../download.html">Download</a> page.</li>
 <li><code>2 GB</code> of memory is recommended for a low traffic production server.
   Spam/Virus scanning will take most system resource.</li>
+<li>Make sure 3 UID/GID are not used by other user/group: 2000, 2001, 2002.</li>
 </ul>
 <p>Note: All packages will be installed from ports tree.</p>
 <h2 id="preparations">Preparations</h2>
diff --git a/html/install.iredmail.on.freebsd.with.jail.html b/html/install.iredmail.on.freebsd.with.jail.html
index 071b74db..d5d3f1f0 100644
--- a/html/install.iredmail.on.freebsd.with.jail.html
+++ b/html/install.iredmail.on.freebsd.with.jail.html
@@ -66,6 +66,7 @@ and it may not be working as expected.</p>
 <ul>
 <li>The latest stable release of iRedMail. You can download it here: http://www.iredmail.org/download.html</li>
 <li>Port <code>sysutils/ezjail</code> for FreeBSD.</li>
+<li>Make sure 3 UID/GID are not used by other user/group: 2000, 2001, 2002.</li>
 </ul>
 <h2 id="preparations">Preparations</h2>
 <h3 id="install-sysutilsezjail-and-add-required-settings">Install sysutils/ezjail and add required settings</h3>
diff --git a/html/install.iredmail.on.openbsd.html b/html/install.iredmail.on.openbsd.html
index a6a41501..a90def0f 100644
--- a/html/install.iredmail.on.openbsd.html
+++ b/html/install.iredmail.on.openbsd.html
@@ -62,6 +62,9 @@ modifying, and it may not be working as expected.</p>
 <li>xbase[XX].tgz</li>
 </ul>
 </li>
+<li>
+<p>Make sure 3 UID/GID are not used by other user/group: 2000, 2001, 2002.</p>
+</li>
 </ul>
 <div class="admonition note">
 <p class="admonition-title">Note</p>
diff --git a/html/install.iredmail.on.rhel.html b/html/install.iredmail.on.rhel.html
index d2a16962..3c31f96e 100644
--- a/html/install.iredmail.on.rhel.html
+++ b/html/install.iredmail.on.rhel.html
@@ -56,6 +56,7 @@ modifying, and it may not be working as expected.</p>
   <a href="../download.html">Download</a> page.</li>
 <li><code>2 GB</code> of memory is recommended for a low traffic production server.
   Spam/Virus scanning will take most system resource.</li>
+<li>Make sure 3 UID/GID are not used by other user/group: 2000, 2001, 2002.</li>
 </ul>
 <h2 id="preparations">Preparations</h2>
 <h3 id="set-a-fully-qualified-domain-name-fqdn-hostname-on-your-server">Set a fully qualified domain name (FQDN) hostname on your server</h3>