Convert POP3 to IMAP tiscali

Convert POP3 email to IMAP? I tried to convert my POP3 email account to IMAP as I need to access my messages from several devices. I was able to set up the IMAP successfully on my iPhone, but entering the same identical account information into eM Client doesn’t work as the server will not authorise the connection (5.7.8 Error: authentication failed)?
Any ideas?