The External Mail -> In Mail page tells VPOP3 how to download mail from your ISP (or other external mail source). You can have as many of these as you want (except in the Home User licence version which allows a maximum of 5 In Mail methods)
Read
about the relationship between Connections,
In Mail and Out
Mail.

VPOP3 can get mail using either the POP3, SMTP or ODMR protocols (see here for a description of these protocols if you’re interested) or the VPOP3 File Transfer method.
VPOP3 has more control over which messages it retrieves when using the POP3 protocol. If you need to use the SMTP protocol, then certain facilities (such as limiting the size of retrieved messages, leaving mail on server, using download rules and using special routing methods) aren't available, but SMTP rules may help you to achieve something similar.
To add/remove In Mail methods, use the External Mail -> In Mail Selection page.
Each In Mail method has a name. This name will be used if VPOP3 reports any errors when using the configuration, but it does not have any real significance - so it is impossible to set the 'In Mail Name' to an incorrect value. To make it easier to keep track of which configuration is which, it is best to use a meaningful name, such as the ISP name and/or the ISP email account name.
Next you choose which method you want VPOP3 to use for getting mail, either POP3, SMTP, ODMR or VPOP3 File Transfer. When you select one of these methods, the relevant options will be shown on the page.
You can enable or disable an Incoming Mail configuration without having to remove it totally using the Enable this In Mail setting checkbox.
The Use this In Mail setting with these Connections list tells VPOP3 which Connections VPOP3 can use to connect to this In Mail method. If any of the selected Connections are started by VPOP3, then this Incoming Mail configuration will be used. If a Connection which is not selected is started by VPOP3, then this Incoming Mail configuration will NOT be used. Note that at least one Connection needs to be selected.
For the protocol specific options, use the appropriate link below: