Hi I have a mail server running on an internal networked Asustor NAS with Thunderbird on the same network on a user PC. Thunderbird picks up the domain and the mail server IMAP settings with the green accept bar. When clicking on Inbox for the newly created Thunderbird account, it asks for the password which is the same for the NAS access user and mail server user account. Password is correct. Message comes back "Login to server xxxx.xxxxx.com with username xxxxx failed" I have tried the connection on recommended IMAP settings (STARTTLS) as well as trying SSL/TLS and an unsecure connection. Port numbers have been changed according to security. Same error message. Mail server has POP3/IMAP/SMTP activated. I have added the domain certificate to Thunderbird through the internal IP:port address. I did notice a hack attempt when entering the xxx.com domain as the certificate location but overcame that by pointing the certificate location through a IP:port address to the NAS address. Certificate is loaded on user PC so connection is secure Not sure why it picks up the mail server and mail settings but then prevents login. Is Thunderbird referencing the mail server to the externally registered domain instead of the locally held mail server? Tried the local IP address as the mail server but Thunderbird rejects that as well replying "Enter a valid server name" Don't think it is a firewall setting? If Thunderbird is pointing to the external domain and picking up MX records, how do I point it to the local IP address where the Asustor NAS mail server is kept? Any help appreciated. Thanks