The mailing list for listmasters using Sympa

[Adam Bernstein <address@concealed>]

>  From my testing, I can see that if a message is sent to multiple Sympa 
> lists and a recipient is a member of more than one of these lists, only 
> one copy of the message is received.

Nope, it doesn't have any way to de-duplicate deliveries like that. 
Subscriber to multiple lists receives a copy from each one.  Must be 
something else going on in your testing.

     ab