On 28 Oct 2015, at 4:04, Marco Stoecker wrote:
As I understand now, the mail from the sender (machine Klamotte) is
delivered to the smtp server from web.de which than is delivered to
1und1 (mx.kundenserver).
Yes. The second "hop" (between web.de and mx.kundenserver.de) occurs 5
times, once for each of 5 target addresses:
ak-lei...@waldorfkindergarten-erlangen.de
vorst...@waldorfkindergarten-erlangen.de
kolleg...@waldorfkindergarten-erlangen.de
gruppensprec...@waldorfkindergarten-erlangen.de
beis...@waldorfkindergarten-erlangen.de
mx.kundenserver.de apparently is delivering mail for all of those
addresses to mailmanser...@waldorfkindergarten-erlangen.de, as shown in
the third ) Received header line in each set you posted (counting
bottom->top, which is the order in which they are added.)
From that point onward there are 5 distinct messages.
If those are 5 different mailing lists, subscribers to multiple lists
will receive multiple copies.
From there fetchmail is getting it
Getting *them*: fetchmail retrieved 5 distinct messages. Your Received
headers show that; the lines added to the 5 messages by fetchmail were
spread out over a 38-second range.
and delivered it to my postfix server, which than delivered it to
mailman. After mailman handled it, it is than sending to the mailing
list recipients vie postfix again.
If postfix already gets 5 messages, than I will check then handover
from fetchmail to postfix and also the message, before it gets to
fetchmail.
This seems to me like it was entirely the work of the *sender* of that
message. A single message was sent to 5 mailing list addresses and it
got delivered to the subscribers of each of 5 mailing lists. This is a
highly predictable (i.e.: perfectly normal) pattern of behavior by
Mailman & Postfix.
If you want the duplication to stop, get the sender to stop sending to
multiple lists. It is entirely that simple and that difficult. If you
want a one-copy-per-subscriber mechanism to send one message to multiple
overlapping lists via Mailman, there is a way to do that with a parent
list in Mailman that merges in multiple subordinate lists and
de-duplicates the subscribers.
