Got to make a note of this support KB from Microsoft
I can never remember how to find it when I need it. Outlook keeps prompting for the POP3 email password. It appears to have something stored - you can see the password stars - it authenticates when you type it in. Then is doesn't remember for the next Outlook session when you restart.
Skip ahead to that section about removing the Protected Storage System provider subkey (not the main key!)
Essentially you're looking for
HKCU\Software\Microsoft\Protected Storage System Provider
then look at the subkeys which are similar to
one for each identity.
Export as a backup then remove that subkey. Re-enter user/password and click the remember password tick box.