FAQ: How does the Maximum Outbound Connections setting work?
Exchange Connector is designed to download from multiple POP3 mailboxes simultaneously to maximize performance when there are a large number of mailboxes. However, some firewalls prevent an application from making more than a specific number of simultaneous outbound network connections. Additionally, some ISPs restrict the number of simultaneous connections allowed to their mail servers.
The maximum outbound connections setting allows you to control how many simultaneous outbound connections will be made by Exchange Connector. The default setting is 5. Increasing this number will improve performance if there are more than 5 mailboxes and there is no firewall restriction. However, if you receive a large number of error messages in the designated administrator mailbox, you should try reducing the maximum number of outbound connections and increasing the POP3 server timeout.