What does no immediate delivery: too many messages received in one SMTP connection mean?

An SMTP client may send any number of messages down a single SMTP connection to a server. Initially, an Exim server starts up a delivery process as soon as a message is received. However, in order not to start up too many processes when lots of messages are arriving (typically after a period of downtime), it stops doing immediate delivery after a certain number of messages have arrived down the same connection. The threshold is set by smtp_accept_queue_per_connection, and the default value is 10. On large systems, the value should be increased. If you are running a dial-in host and expecting to get all your mail down a single SMTP connection, then you can disable the limit altogether by setting the value to zero.

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