diff --git a/en_US/howto/track.user.last.login.md b/en_US/howto/track.user.last.login.md
index b11bc8d1..28e4228e 100644
--- a/en_US/howto/track.user.last.login.md
+++ b/en_US/howto/track.user.last.login.md
@@ -2,6 +2,16 @@
 
 [TOC]
 
+!!! warning
+
+    This feature is not available for PostgreSQL backend due to Dovecot does
+    not yet support updating existing SQL record on conflict primary key.
+
+    Relevent posts in Dovecot mailing lists:
+
+    - <https://marc.info/?t=155411531600001&r=1&w=2>
+    - <https://marc.info/?t=155826327900001&r=1&w=2>
+
 Dovecot ships a `last_login` plugin since Dovecot-2.2.14, it can be used to
 easily save and update user's last-login timestamp in SQL database.
 
diff --git a/html/track.user.last.login.html b/html/track.user.last.login.html
index 4f72d551..9eb49a92 100644
--- a/html/track.user.last.login.html
+++ b/html/track.user.last.login.html
@@ -27,6 +27,16 @@
 </li>
 </ul>
 </div>
+<div class="admonition warning">
+<p class="admonition-title">Warning</p>
+<p>This feature is not available for PostgreSQL backend due to Dovecot does
+not yet support updating existing SQL record on conflict primary key.</p>
+<p>Relevent posts in Dovecot mailing lists:</p>
+<ul>
+<li><a href="https://marc.info/?t=155411531600001&amp;r=1&amp;w=2">https://marc.info/?t=155411531600001&amp;r=1&amp;w=2</a></li>
+<li><a href="https://marc.info/?t=155826327900001&amp;r=1&amp;w=2">https://marc.info/?t=155826327900001&amp;r=1&amp;w=2</a></li>
+</ul>
+</div>
 <p>Dovecot ships a <code>last_login</code> plugin since Dovecot-2.2.14, it can be used to
 easily save and update user's last-login timestamp in SQL database.</p>
 <div class="admonition attention">