If it says the user name or password is wrong then this can mean a couple of things. The password or username is incorrect. Note: An additional mailbox username looks like this: account username+mailbox name. Test by logging on to webmail account. If you get access then you know the password is correct. Assuming both password and username are correct, but not correct for the server settings you have chosen to use. https://www.plus.net/help/email-guides/how-to-set-up-plusnet-email/ 'Menu icon' > 'New Message' > 'Existing mail account' * Enter name * Enter username * Enter password * select checkbox to remember password * Click on 'Continue Thunderbird attempts to locate server settings. * Click on 'Manual config' button Make sure the correct Type of server is selected eg: POP or IMAP Change any setting as required. POP server settings: * Incoming server name : mail.plus.net * Incoming Port : 110 * Connection Security: None * Authentication Method: Password IMAP server Settings: * Incoming server name : imap.plus.net * Incoming port 143 * Connection Security: None * Authentication Method: Password * Outgoing server name : relay.plus.net * Outgoing port : 587 * Connection Security: None * Authentication Method: Password SMTP Authentication (only needed if you're sending emails from a non-Plusnet Internet connection)* Yes Good visual help here: https://www.plus.net/help/archive/email/thunderbird-setup/ Note ports have changed as port 25 for outgoing is often rejected by servers.