Incredimail email accounts setup with Plusnet mailboxes.?

[#1]

Can anyone explain the correct entries in Incredimail accounts setup for use with Plusnet Mailboxes.?

[#2]

Which fields are you unsure about?
If you go to the Email setup guides help page and click the I just want to see the email settings link in the line before the Mobile devices header a pop-up will display containing all the settings. This covers both the default mailbox and additional ones.

[#3]

Might be worth you posting a screengrab of the settings the program is asking you for. Regardless of the client you're using, the settings required to access your mailbox are likely to be the same. You can see those by clicking the 'I just want to see the email settings' hyperlink here.
You'll also need to disable any options to use SSL/TLS or secure connections.
Edit: spraxyt beat me to it. We should look at getting that settings page linkable.

[#4]

Incredimail has some disreputable friends and he is likely to invite them over for a party on your computer.  I would steer well clear.