diff --git a/docs/usage.rst b/docs/usage.rst
index ea7f8e86d9de33ca3dcc39fc41eb8faa3c49e840..ecfc0984d1dcecb5f25da43d0cff6003532cb543 100644
--- a/docs/usage.rst
+++ b/docs/usage.rst
@@ -810,7 +810,9 @@ role.
      swaks --to jane.doe@example.com --server comms.example.com
 
   Of course, free feel to also test out the mail server using any mail client of
-  your choice.
+  your choice. When doing so, use port 587 for SMTP. Port 25 is reserved for
+  unauthenticated server-to-server mail deliveries. TLS has also been hardened
+  on port 587 to allow only TLSv1.2 and PFS ciphers.
 
 
 Setting-up mail relaying from web and backup servers