Authentication problem using username and password with new eM Client?
Authentication problems can be the result of incorrect settings.
Go to Menu > Tools > Accounts, and check your IMAP or POP3 settings.
SMTP
Port 587 = Force usage of SSL/TLS
Port 25 = Use SSL/TLS if available
Port 465 = Use SSL/TLS on special port (legacy)
IMAP
Port 993 = Use SSL/TLS on special port (legacy)
Port 143 = Use SSL/TLS if available
POP3
Port 995 = Use SSL/TLS on special port (legacy)
Port 110 = Use SSL/TLS if available
These are the correct combinations of port and security policy. The underlined ones are the best option for security if your server supports them. SMTP port 465 was reassigned and should no longer be used for SMTP, though many mail providers still recommend and use it.