diff --git a/DKIM-how-to.md b/DKIM-how-to.md
index a2bb34d..8353eac 100644
--- a/DKIM-how-to.md
+++ b/DKIM-how-to.md
@@ -22,4 +22,9 @@ Signing in Postfix
 * SpamAssassin version 3.4.2 (running on Perl version 5.28.1)
 * Postfix 3.4.5
 * BIND 9.10.3-P4-Debian
-* OpenDKIM v2.11.0
\ No newline at end of file
+* OpenDKIM v2.11.0
+
+**Assumptions**
+* DNSSEC is used
+* Mail server is operational
+* Software packages are already installed
\ No newline at end of file