On Fri, Mar 05, 2021 at 04:25:38AM -0500, Viktor Dukhovni wrote:
> There are only two common ways a message without duplicated recipients
> gets delivered to the same mailbox twice:
>
> 1. Address rewriting (including BCC maps) duplicates a recipient,
> and "enable_original_recipient" is not set to "no".
>
> 2. A message with multiple recipients is delivered via multiple
> transport:nexthop combinations, the separate messages then
> get augmented with (or rewritten to) a common recipient.
>
> A third less common way is via local(8) aliases, because local
> delivery splits the envelope to one recipient at a time before
> alias(5) expansion.
I glossed over one detail in (2), the envelope also splits when a
message has more recipients than the transport's destination recipient
limit. I generally give content filter transports a much higher than
default recipient limit, e.g. 1000, rather than the default of 50.
The OP's use-case had just a handful of recipients, so this is not
an immediate a concern in this thread.
--
Viktor.
