From e0e9b28c057da3b971953f2ab2c97aab07b31110 Mon Sep 17 00:00:00 2001
From: Christoph Wurst <1374172+ChristophWurst@users.noreply.github.com>
Date: Wed, 27 May 2026 09:10:10 +0200
Subject: [PATCH] docs(admin): document smtp_saves_sent config for Exchange
 duplicate prevention

Signed-off-by: Christoph Wurst <1374172+ChristophWurst@users.noreply.github.com>
---
 admin_manual/groupware/mail.rst | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/admin_manual/groupware/mail.rst b/admin_manual/groupware/mail.rst
index ccc85aadb9b..4772ba61b49 100644
--- a/admin_manual/groupware/mail.rst
+++ b/admin_manual/groupware/mail.rst
@@ -30,6 +30,23 @@ To enable anti-abuse alerts, you'll have to set a few configuration options :doc
     # Alert when more than 100 messages are sent in one day
     occ config:app:set mail abuse_number_of_messages_per_1d --value=100
 
+Avoid duplicate sent messages (Exchange / Office 365)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. versionadded:: 5.8 Nextcloud 32 or newer
+
+Microsoft Exchange and Office 365 automatically save a copy of sent messages to the *Sent* folder
+on the server. If the Mail app saves a copy too, users will see duplicates in their *Sent* folder.
+
+To avoid this, you can enable a check that skips the client-side copy when the server has already
+saved one. The check is disabled by default as it adds an IMAP round-trip to every send::
+
+    occ config:app:set mail smtp_saves_sent --value=true
+
+To disable it again::
+
+    occ config:app:delete mail smtp_saves_sent
+
 Attachment size limit
 ^^^^^^^^^^^^^^^^^^^^^