More headers preserved

For cleartext: To, CC, In-Reply-To, References

For Chatmail future expansion, allow Chat-*

cmdeploy/src/cmdeploy/postfix/lmtp_header_cleanup

@@ -2,12 +2,16 @@
 # that must be retained for functionality and compatibility reasons 
 /^From:/            DUNNO
 /^Message-Id:/      DUNNO
-/^Chat-Is-Post-Message:/      DUNNO
+/^Chat-/            DUNNO
 /^Content-Type:/    DUNNO
 
 # For receiving clear-text messages (still supported in May 2026)
 /^Subject:/         DUNNO
 /^Date:/            DUNNO
+/^To:/              DUNNO
+/^CC:/              DUNNO
+/^References:/      DUNNO
+/^In-Reply-To:/     DUNNO
 
 # Senders might support Autocrypt 1 but not RFC9788 (Header Protection) 
 /^Autocrypt:/            DUNNO