Enable VERP for (some) outbound emails

Improve bounce detection.

Also reduce the number of recipients per single SMTP delivery.

roles/mailman/templates/mm_cfg.py.j2

@@ -113,7 +113,7 @@ DEFAULT_REPLY_GOES_TO_LIST = 0
 DEFAULT_MAX_DAYS_TO_HOLD = 15
 
 # rimuove le firme Dkim e Dk dalle mail in entrata a mailman
-REMOVE_DKIM_HEADERS = 'YES'
+REMOVE_DKIM_HEADERS = Yes
 
 
 #-------------------------------------------------------------
@@ -141,11 +141,14 @@ ARCHIVE_HTML_SANITIZER = 0
 # 3 = Discard
 DEFAULT_GENERIC_NONMEMBER_ACTION = 2
 
-# added by ale+blicero to limit recipient per send and avoid spam limit measures
-SMTP_MAX_RCPTS = 50
+# Enable VERP probes for better bounce detection, one in 10 emails.
+VERP_PROBES = Yes
+VERP_CONFIRMATIONS = Yes
+VERP_DELIVERY_INTERVAL = 10
 
-# Note - if you're looking for something that is imported from mm_cfg, but you
-# didn't find it above, it's probably in /usr/lib/mailman/Mailman/Defaults.py.
+# Limit recipient per send, avoid spam limit measures and limit blast
+# radius from delivery failures.
+SMTP_MAX_RCPTS = 10
 
 DEFAULT_SUBSCRIBE_POLICY = 3
 DEFAULT_LIST_ADVERTISED = No