add bits of documentation for new environment variable

docs/compose/.env

@@ -102,6 +102,9 @@ COMPRESSION=
 # change compression-level, default: 6 (value: 1-9)
 COMPRESSION_LEVEL=
 
+# IMAP full-text search is enabled by default. Set the following variable to off in order to disable the feature.
+# FULL_TEXT_SEARCH=off
+
 ###################################
 # Web settings
 ###################################

docs/configuration.rst

@@ -83,6 +83,9 @@ later classify incoming mail based on the custom part.
 The ``DMARC_RUA`` and ``DMARC_RUF`` are DMARC protocol specific values. They hold
 the localpart for DMARC rua and ruf email addresses.
 
+Full-text search is enabled for IMAP is enabled by default. This feature can be disabled
+(e.g. for performance reasons) by setting the optional variable ``FULL_TEXT_SEARCH`` to ``off``.
+
 Web settings
 ------------
 

setup/flavors/compose/mailu.env

@@ -91,6 +91,9 @@ COMPRESSION={{ compression }}
 # change compression-level, default: 6 (value: 1-9)
 COMPRESSION_LEVEL={{ compression_level }}
 
+# IMAP full-text search is enabled by default. Set the following variable to off in order to disable the feature.
+# FULL_TEXT_SEARCH=off
+
 ###################################
 # Web settings
 ###################################