diff --git a/deploy/mailu/mailu.env.example b/deploy/mailu/mailu.env.example
index 15f4836..6c460a8 100644
--- a/deploy/mailu/mailu.env.example
+++ b/deploy/mailu/mailu.env.example
@@ -37,6 +37,16 @@ BIND_ADDRESS4=127.0.0.1
 SUBNET=192.168.203.0/24
 MESSAGE_SIZE_LIMIT=52428800           # 50 MB
 
+# --- Addressing --------------------------------------------------------------
+# Plus-addressing (subaddressing): deliver mail sent to <name>+<tag>@ into the
+# <name>@ mailbox (keeping the +tag in the To: header for filtering) instead of
+# bouncing it as an unknown recipient. Required by qaaas.dev's packages/mail,
+# which mints throwaway addresses like chovy+run-42@bbs.profullstack.com off the
+# single chovy@ mailbox. NOTE: this affects DELIVERY only — it does NOT let
+# <name>+<tag>@ be used as a LOGIN (Mailu authenticates the exact address; log
+# into webmail as the base <name>@ and all +tagged mail is already there).
+RECIPIENT_DELIMITER=+
+
 # --- Gateway (the BBS reads/sends on behalf of members) ----------------------
 # A Dovecot master user lets the agentbbs gateway open any member's mailbox with
 # one secret (login "<name>*<master>"). Created by deploy/mailu/provision-mailbox.sh.