I have made 3 or 4 attempts to install em Client (various versions) and every time it will not recognize my internet provider password, though it accepts my email address. Yet em Client write to me at that address. I have a suspicion that Microsoft are preventing proper installation of a rival product. I use Windows Mail at present.
Did eM Client install correctly?
Do you mean your email account password?
Who is your email provider?
Yes. My Internet / Email account provider is Talk Talk
Maybe login to the TalkTalk website and change your password on your email account to something simple. Then back in eM Client add the account again with the new simple password. If that works, you know you have the correct credentials and eM Client is working. You can then go back to the web interface and reset your password to something more secure. When you restart eM Client it will ask you for the new password.