max_deliveries_per_connection — maximum number of messages to deliver before closing a connection
max_deliveries_per_connection = 0
The maximum number of messages that will be sent over a single SMTP connection. This option limits successful deliveries only. If you wish to limit the number of attempted RCPT TO commands that are sent, use
max_deliveries_per_connection is configurable globally, in the binding scope and on a per-domain basis. If set to
0 (the default), then no maximum limit will be enforced.
max_deliveries_per_connection is valid in the binding, binding_group, domain and global scopes.