There seems to be confusion here.

A bounce (or "Non-delivery notification" or "Delivery status notification" 
which is something similar but with a fixed format) is just a message detailing 
the non-delivery, or successful or delayed deliveries in some systems and 
especially with use of Delivery Status Notifications, about a message that was 
sent.

When a mailing list manager (the bit of software that runs a mailing list) 
receives a bounce message, it must somehow determine the cause.  It parses the 
bounce, which is often different with different mail software, trying to work 
out which member of its lists are responsible for the errors in delivery of the 
mailing list messages.  Modern mailing list software does a fairly good job of 
this, but it's still fiendishly tricky.  A scheme, once thought very difficult 
and expensive, is now being reconsidered for making this process more-or-less 
automatic and guaranteed to work, that being Variable Envelope Return Path 
(VERP): the idea is that the mailing list software, instead of sending out one 
message to many users, sends out one message to each user, but sets the return 
address to a unique address, per sender, per message.  That way, the address 
the bounce goes to fingers precisely the subscriber and message implicated in 
the original delivery error.  The BrailleNote list does not use VERP.

Which brings us to Mailman, used by HumanWare.  It's decent enough mailing list 
management software, and it tries very hard to forgive temporary delivery 
errors, as distinct from permanent errors, that is, those which cannot be 
recovered from, like an invalid address.  It uses a bounce score system.  Each 
time a temporary problem occurs, the score goes up by 0.5.  Each time a 
permanent error occurs, the score goes up by 1.0.  A maximum score (set by the 
list owner) determines some final action to be taken, which defaults to 
disabling the subscription and then sending out periodic reminders, but it can 
include immediate unsubscription without further fuss.

So, in summary, the reason why you see what you do is that you (or your mail 
server) is losing posts (or accepting them but sending a bounce, which is 
highly broken, but it's possible) for the BrailleNote list.  The list software 
gets the bounces back, and your score is adjusted accordingly to match the type 
and number of bounces, and if no bounces occur for a while, automatically 
reset.  Also note, that the bounce can happen anywhere; if you send a message 
to the list and immediately your bounce score goes up, it's possible that 
HumanWare's own mail server is rejecting the post sent for distribution in the 
process of doing so.  However, I haven't seen this problem, so I think it more 
likely that the subscribers themselves are causing the bounces (their ISP's 
stupid spam filters, for instance).

Hope this has helped somebody somewhere. :-)

Cheers,
Sabahattin

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