Document that Elasticsearch/OpenSearch user search does not match email address

source/administration-guide/scale/common-configure-mattermost-for-enterprise-search.rst

@@ -50,3 +50,4 @@ Enterprise search limitations
 1. Elasticsearch and AWS OpenSearch uses a standard selection of "stop words" to keep search results relevant. Results for the following words will not be returned: "a", "an", "and", "are", "as", "at", "be", "but", "by", "for", "if", "in", "into", "is", "it", "no", "not", "of", "on", "or", "such", "that", "the", "their", "then", "there", "these", "they", "this", "to", "was", "will", and "with".
 2. Searching stop words in quotes returns more results than just the searched terms (`ticket <https://mattermost.atlassian.net/browse/MM-7216>`__).
 3. By default, search results are limited to a user's team and channel membership. This is enforced by the Mattermost server. The entities are indexed in Elasticsearch or AWS OpenSearch in a way that allows Mattermost to filter them when querying, so the Mattermost server narrows down the results on every Elasticsearch or AWS OpenSearch request applying those filters. From Mattermost v11.6, admins can :ref:`allow searching public channels without membership <administration-guide/configure/environment-configuration-settings:allow searching public channels without membership>` so that users can find messages in public channels they haven't joined, scoped to teams they belong to.
+4. User search and autocomplete served by Elasticsearch or AWS OpenSearch match on username, nickname, and first and last name only. Email addresses aren't indexed, so users can't be found by email address. User searches served from the database continue to match on email address, including the **System Console > User Management > Users** list, and channel and team member searches. For users who aren't system admins, email address matching also requires :ref:`Show email address <administration-guide/configure/site-configuration-settings:show email address>` to be enabled.

source/administration-guide/upgrade/admin-onboarding-tasks.rst

@@ -143,6 +143,6 @@ Then, enable batched email notifications by setting **System Console > Notificat
 
 **9. Enable Elasticsearch**
 
-Mattermost Enterprise customers can enable :doc:`enterprise search </administration-guide/scale/enterprise-search>` for optimized search performance at enterprise-scale. Both Elasticsearch and AWS OpenSearch solve many known issues with full text database search, such as dots, dashes, and email addresses returning unexpected results.
+Mattermost Enterprise customers can enable :doc:`enterprise search </administration-guide/scale/enterprise-search>` for optimized search performance at enterprise-scale. Both Elasticsearch and AWS OpenSearch solve many known issues with full text message search in the database, such as dots, dashes, and email addresses returning unexpected results. Before enabling, review the :ref:`enterprise search limitations <administration-guide/scale/common-configure-mattermost-for-enterprise-search:enterprise search limitations>`, as some user search behavior differs from database search.
 
 Enable Elasticsearch by setting **System Console > Elasticsearch > Enable Indexing** to **true**. See the :ref:`Elasticsearch <administration-guide/configure/environment-configuration-settings:enterprise search>` configuration settings documentation for details. Enabling Elasticsearch requires :ref:`setting up an Elasticsearch server <administration-guide/scale/elasticsearch-setup:set up elasticsearch>`.