It is always necessary to supply the email mailbox name and password when collecting mail. That applies with any email client, not just Outlook. Nothing has changed for years in this respect.
Usually the required information is entered when the email account details are set up in the email client (Outlook in your case). If these login details change (e.g. because the Member Centre password is changed) the details in Outlook need to be updated. If that is not done, I think the user is prompted for the correct password each time Outlook starts - as was happening for you. My guess is that this has gone away because the account setting in Outlook has been updated with the correct password information, not because anything has changed at the Plusnet end. Or alternatively that the Member Centre password has been changed to the one that matches that set up in Outlook.
David
