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.
> 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.
--
Viktor.
