One of the frequent causes of confusion with VPOP3 is the relationship between Connections, In Mail and Out Mail.
This confusion is because the VPOP3 scheme isn't as limiting as normal email software. It allows great flexibility for when you have several Internet provider accounts.
A Connection is a method VPOP3 uses to connect to the Internet.
An In Mail method tells VPOP3 how to collect incoming email. These can be linked to one or more Connections.
An Out Mail method tells VPOP3 how to send outgoing mail. For each Connection there is a corresponding Out Mail configuration. This is because many ISPs are now implementing anti-relay filters which prevent you sending outgoing mail through them unless you have dialed into their modems.
Whenever VPOP3 connects to a Connection, it will process the associated Out Mail configuration, and all In Mail configurations which are linked to this Connection before disconnecting.
Let us say that you have two Internet provider accounts.
You will typically tell VPOP3 about these two accounts by creating two Connection entries, one for each ISP. These will tell VPOP3 how to connect to the Internet using each of those dial-up accounts.
For each of these Connection entries, you will create a corresponding Out Mail entry, which tells VPOP3 how to send outgoing mail when it is connected to one or the other of these dial-up account.
You will also typically tell VPOP3 about these two accounts by creating two In Mail entries, one for each ISP. These will tell VPOP3 how to collect your email from both of those Internet email accounts,
The simplest thing to do is to simply tell VPOP3 to link the ISP1 In Mail configuration to the ISP1 Connection, and the ISP2 In Mail to the ISP2 Connection. However, if you do that, then to collect email from both ISP1 and ISP2, VPOP3 will have to make two dial-up connections to the Internet, which will be slow and costly.
Instead, you can tell VPOP3 to link the ISP1 In Mail connection to BOTH Connections, and similarly with the ISP2 In Mail configuration. Most Internet providers allow you to have access to your POP3 mailboxes from anywhere on the Internet, so VPOP3 can easily access the ISP1 POP3 mailbox when it is connected to the Internet using ISP2.
When you do this, then you can tell VPOP3 to either connect using ISP1 or to connect using ISP2, in either case it will collect mail from both your ISP mailboxes.