Document credential separation: Nextcloud Mail uses different IMAP/SMTP credentials

README.md

@@ -173,6 +173,13 @@ nextcloud-calendar --op list-events
 
 ### Email (IMAP/SMTP)
 
+**⚠️ Important:** The Nextcloud Mail integration uses **different credentials** from other Nextcloud tools (Files, Contacts, Calendar).
+
+- **Other tools**: Use Nextcloud API credentials (server URL + username + API token)
+- **Mail**: Uses IMAP/SMTP credentials (IMAP hostname, SMTP hostname, username, password)
+
+These are separate authentication systems with different credentials. See `skills/nextcloud-mail/SKILL.md` for details.
+
 ```bash
 # List folders
 nextcloud-mail --op list-folders