diff --git a/wildduck/README.md b/wildduck/README.md
index 8158285..4714e69 100644
--- a/wildduck/README.md
+++ b/wildduck/README.md
@@ -2,3 +2,23 @@
 
 This application is managed by
 [ArgoCD](https://argocd.k-space.ee/applications/argocd/wildduck)
+
+The mail stack consists of several moving parts:
+
+* Haraka with several plugins
+  * Wildduck plugin to handle incoming mail on port 25 of mail.k-space.ee
+  * Fight spam with Rspamd
+  * Fight viruses with ClamAV
+* Wildduck
+  * Provide API for interfacing with other systems such as
+    Wildduck webmail,
+    Wildflock e-mail alias generator and
+    Wildduck Kubernetes operator which deals with account provisioning
+  * Provide IMAP endpoint for accessing mailbox with traditional
+    MUA (mail user agents): Android, iPhone, Thunderbird, Evolution etc
+* ZoneMTA for handling outbound mail
+  * Including mail submission from MUA with the help of Wildduck plugin
+
+Outside Kubernetes there is NAT rule on the Mikrotik router
+which rewrites source IP of any TCP port 25 headed traffic to
+originate from the IP address of the mail exchange.