front: advertise real capabilites of mail-backends

core/nginx/conf/nginx.conf

@@ -193,6 +193,11 @@ mail {
     ssl_session_cache shared:SSLMAIL:50m;
     {% endif %}
 
+    # Advertise real capabilites of backends (postfix/dovecot)
+    smtp_capabilities PIPELINING SIZE {{ MESSAGE_SIZE_LIMIT }} ETRN ENHANCEDSTATUSCODES 8BITMIME DSN CHUNKING;
+    pop3_capabilities TOP UIDL RESP-CODES PIPELINING AUTH-RESP-CODE USER;
+    imap_capabilities IMAP4 IMAP4rev1 UIDPLUS SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+;
+
     # Default SMTP server for the webmail (no encryption, but authentication)
     server {
       listen 10025;