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3. Parallel delivery to the same destination

Local destination concurrency limit

How many parallel deliveries to the same user or domain? With local delivery, it does not make sense to do massively parallel delivery to the same user, because mailbox updates must happen sequentially, and expensive pipelines in .forward files can cause disasters when too many are run at the same time. With SMTP deliveries, 10 simultaneous connections to the same domain could be sufficient to raise eyebrows.

Each message delivery transport has its XXX_destination_concurrency_limit parameter. The default is is taken from the "Default destination concurrency limit" option.

This option sets the "local_destination_concurrency_limit" postfix variable.

Default destination concurrency limit

The "Default destination concurrency limit" option specifies a default limit on the number of parallel deliveries to the same destination. This is the default limit for delivery via SMTP, via the local delivery agent and via the pipe mailer. This option sets the "default_destination_concurrency_limit" postfix variable.

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