diff --git a/administrator/components/com_admin/sql/updates/postgresql/3.9.15-2020-01-08.sql b/administrator/components/com_admin/sql/updates/postgresql/3.9.15-2020-01-08.sql
new file mode 100644
index 0000000000000..a25179f9b38d1
--- /dev/null
+++ b/administrator/components/com_admin/sql/updates/postgresql/3.9.15-2020-01-08.sql
@@ -0,0 +1 @@
+CREATE INDEX "#__users_email_lower" ON "#__users" (lower("email"));
diff --git a/administrator/components/com_privacy/models/export.php b/administrator/components/com_privacy/models/export.php
index 0bb8e5acac71d..89d323638d59e 100644
--- a/administrator/components/com_privacy/models/export.php
+++ b/administrator/components/com_privacy/models/export.php
@@ -69,7 +69,7 @@ public function collectDataForExportRequest($id = null)
 			$db->getQuery(true)
 				->select('id')
 				->from($db->quoteName('#__users'))
-				->where($db->quoteName('email') . ' = ' . $db->quote($table->email)),
+				->where('LOWER(' . $db->quoteName('email') . ') = LOWER(' . $db->quote($table->email) . ')'),
 			0,
 			1
 		)->loadResult();
@@ -164,7 +164,7 @@ public function emailDataExport($id = null)
 			$db->getQuery(true)
 				->select('id')
 				->from($db->quoteName('#__users'))
-				->where($db->quoteName('email') . ' = ' . $db->quote($table->email)),
+				->where('LOWER(' . $db->quoteName('email') . ') = LOWER(' . $db->quote($table->email) . ')'),
 			0,
 			1
 		)->loadResult();
diff --git a/administrator/components/com_privacy/models/remove.php b/administrator/components/com_privacy/models/remove.php
index 86e1d551284b2..75f3e73bc8acd 100644
--- a/administrator/components/com_privacy/models/remove.php
+++ b/administrator/components/com_privacy/models/remove.php
@@ -70,7 +70,7 @@ public function removeDataForRequest($id = null)
 			$db->getQuery(true)
 				->select('id')
 				->from($db->quoteName('#__users'))
-				->where($db->quoteName('email') . ' = ' . $db->quote($table->email)),
+				->where('LOWER(' . $db->quoteName('email') . ') = LOWER(' . $db->quote($table->email) . ')'),
 			0,
 			1
 		)->loadResult();
diff --git a/administrator/components/com_privacy/models/request.php b/administrator/components/com_privacy/models/request.php
index bf3eead939c3e..5c679f5ca3acb 100644
--- a/administrator/components/com_privacy/models/request.php
+++ b/administrator/components/com_privacy/models/request.php
@@ -262,7 +262,7 @@ public function notifyUserAdminCreatedRequest($id)
 			$db->getQuery(true)
 				->select('id')
 				->from($db->quoteName('#__users'))
-				->where($db->quoteName('email') . ' = ' . $db->quote($table->email)),
+				->where('LOWER(' . $db->quoteName('email') . ') = LOWER(' . $db->quote($table->email) . ')'),
 			0,
 			1
 		)->loadResult();
diff --git a/components/com_users/models/remind.php b/components/com_users/models/remind.php
index 967daac122de7..c940c67087410 100644
--- a/components/com_users/models/remind.php
+++ b/components/com_users/models/remind.php
@@ -125,7 +125,7 @@ public function processRemindRequest($data)
 		$query = $db->getQuery(true)
 			->select('*')
 			->from($db->quoteName('#__users'))
-			->where($db->quoteName('email') . ' = ' . $db->quote($data['email']));
+			->where('LOWER(' . $db->quoteName('email') . ') = LOWER(' . $db->quote($data['email']) . ')');
 
 		// Get the user id.
 		$db->setQuery($query);
diff --git a/components/com_users/models/reset.php b/components/com_users/models/reset.php
index d93c49eb491e7..fc9117e1fb41f 100644
--- a/components/com_users/models/reset.php
+++ b/components/com_users/models/reset.php
@@ -379,7 +379,7 @@ public function processResetRequest($data)
 		$query = $db->getQuery(true)
 			->select('id')
 			->from($db->quoteName('#__users'))
-			->where($db->quoteName('email') . ' = ' . $db->quote($data['email']));
+			->where('LOWER(' . $db->quoteName('email') . ') = LOWER(' . $db->quote($data['email']) . ')');
 
 		// Get the user object.
 		$db->setQuery($query);
diff --git a/installation/sql/postgresql/joomla.sql b/installation/sql/postgresql/joomla.sql
index 77cebdbebafcb..54116efe76d21 100644
--- a/installation/sql/postgresql/joomla.sql
+++ b/installation/sql/postgresql/joomla.sql
@@ -2055,6 +2055,7 @@ CREATE INDEX "#__users_idx_name" ON "#__users" ("name");
 CREATE INDEX "#__users_idx_block" ON "#__users" ("block");
 CREATE INDEX "#__users_username" ON "#__users" ("username");
 CREATE INDEX "#__users_email" ON "#__users" ("email");
+CREATE INDEX "#__users_email_lower" ON "#__users" (lower("email"));
 
 COMMENT ON COLUMN "#__users"."lastResetTime" IS 'Date of last password reset';
 COMMENT ON COLUMN "#__users"."resetCount" IS 'Count of password resets since lastResetTime';
diff --git a/libraries/src/Table/User.php b/libraries/src/Table/User.php
index fd35e44864ce3..2527c988b817b 100644
--- a/libraries/src/Table/User.php
+++ b/libraries/src/Table/User.php
@@ -245,7 +245,7 @@ public function check()
 		$query->clear()
 			->select($this->_db->quoteName('id'))
 			->from($this->_db->quoteName('#__users'))
-			->where($this->_db->quoteName('email') . ' = ' . $this->_db->quote($this->email))
+			->where('LOWER(' . $this->_db->quoteName('email') . ') = LOWER(' . $this->_db->quote($this->email) . ')')
 			->where($this->_db->quoteName('id') . ' != ' . (int) $this->id);
 		$this->_db->setQuery($query);
 		$xid = (int) $this->_db->loadResult();
diff --git a/plugins/system/updatenotification/updatenotification.php b/plugins/system/updatenotification/updatenotification.php
index da06897328ed2..c3df4a09f323e 100644
--- a/plugins/system/updatenotification/updatenotification.php
+++ b/plugins/system/updatenotification/updatenotification.php
@@ -366,7 +366,7 @@ private function getSuperUsers($email = null)
 
 			if (!empty($emails))
 			{
-				$query->where($db->qn('email') . 'IN(' . implode(',', $emails) . ')');
+				$query->where('LOWER(' . $db->qn('email') . ') IN(' . implode(',', array_map('strtolower', $emails)) . ')');
 			}
 
 			$db->setQuery($query);