Am 2021-06-10 20:57, schrieb Viktor Dukhovni:
On Thu, Jun 10, 2021 at 04:30:11PM +0200, Michael Storz wrote:
The next possibility would be to split the email into emails with
recipients from the same domain. Unfortunately, Postfix (currently)
has
no way of configuring a relay host and specifying that the email
should
be split according to the same recipient domain.
A socketmap(5) or tcp_table(5) transport(5) table can map each
recipient
domain (e.g., some.domain.example) into a common parent with a wildcard
A
record:
# Domain part of key # Returned result
some.domain.example smtp:[some.domain.example.wild.local]:10025
[ The code performing this mapping should validate the domain syntax,
returning no result for unexpected input syntax. ]
The local nameserver would be authoritative for "wild.local" zone,
which
apart from any zone apex SOA and NS RRs would have:
*.wild.local. IN A 127.0.0.1
In a multi-instance configuration, the input instance could use such
a transport table to split the envelope of every message before handing
it off to the output instance.
Ah, I see: the mapping triggers the normal domain based splitting for
emails routed via MX-/A-records and the wildcard A-record simulates the
relay host. Great idea, a little bit tricky, but it should work. Thanks
Viktor.
The last option is to split the email into single recipient emails.
Then
there is no need to differentiate. You can use either single-instance
or
multi-instance Postfix installations to do this. We use single
instance.
Postfix has the TRANSPORT_destination_recipient_limit option (replace
TRANSPORT with the name of the transport you are using) to split an
email according to the number of recipients. If set to 1, you will
receive single recipient emails.
Worth noting that concurrency limits are then applied per-recipient,
not
per-domain.
