What do you mean, exactly. Is Evolution refusing to add your POP3 password to the set-up of you Mail Host? Or are you trying to use your (given?) POP3 password when starting Evolution?
What do you mean exactly by your POP3 password; is it the password given to you by your provider, for your POP3 account? If so, where are you trying to enter it?
You should use that in the set-up of your Mail Host accounts.
Please expand on what your problem is.
Some email services like Yahoo (free edition) put up road blocks where you can’t send email out through a desktop client unless you upgrade your account. Yahoo Pop3.
Check with your email service provider to ensure they support the service for your account type.
If that’s not the problem try downloading Thunderbird and test the account with that client. If the issue persists It’s not a problem with Evolution.