MAS-WP-0003-T04: IONOS forward results (rejects '=', lower-cases; SRS safe); SCP-6/7

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 252470@bnt-lap001
Assistant-Session: ad628c8f-4be2-4979-94c9-76c7ed6f8241

workplans/MAS-WP-0003-provider-live-test.md

@@ -167,7 +167,7 @@ address and what envelope recipient arrives.
 
 ```task
 id: MAS-WP-0003-T04
-status: todo
+status: progress
 priority: medium
 state_hub_task_id: "97c88b4f-14c3-5f6c-8f31-6b9fc3afd236"
 ```
@@ -176,6 +176,20 @@ Send via one forwarding service (SRS) and one mailing list (VERP). Check
 whether `=` collides with SRS0/VERP encoding, and whether facets survive
 or are stripped.
 
+- 2026-10-18, IONOS mail forward (`mas-fwd@coulomb.social`): the IONOS form
+  refuses `=` in the destination and forces lower case. The operator used
+  `ticket--GS-85QJ8WC09P+comments@`, and `ticket--gs-85qj8wc09p+comments@`
+  arrived at 11:47:06Z from mout.kundenserver.de. The envelope sender was
+  SRS-rewritten (`SRS0=ppc5=II=gmail.com=bernd.worsch@srs2.kundenserver.de`).
+  SRS only touches the sender, so there is no collision with `=` in
+  recipients. The facet survived, and the header To kept the forward
+  address. The gateway saw an opaque target with a facet, and the app
+  correctly declined it (404). This led to SCP-6 (statute-declared `--`
+  separator; the operator endorses the mapping) and SCP-7 (case-robust
+  identifiers).
+  Gmail forwarding: skipped (optional; would only add a second forwarder
+  that accepts `=`). Still open: one mailing list (VERP).
+
 ## Cap total outbound mail
 
 ```task