The server was found but authentication failed
This could mean you might need an eg: app password or a 2 step password instead of your normal password or you have the wrong authentication protocols configured in the manual email setup you chose.
Who is your mail box provider and are you using a POP, IMAP, Exchange, or iCloud manual setup. Also what are the manual mail settings you have tried. Can you update this thread & blank out any personal details.
Also have you tried running the automatic email account wizard & was it the same error when you went through that.
Lastly do you have Windows or Mac OS and what version of eM Client are you using.