diff --git a/conf/srs.conf.sample b/conf/srs.conf.sample
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+++ b/conf/srs.conf.sample
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+# ---
+# - Selective SRS configuration
+# ---
+
+# Domain used as envelope sender domain for SRS rewritten messages.
+#
+# DNS/SPF for this domain must authorize the outgoing mail server.
+#
+# Example:
+#
+#    _SRS_DOMAIN="srs.example.org"
+#
+_SRS_DOMAIN=""