Apple mail outgoing mail server (SMTP) authentication settings

I'm having problems sending outbound apple mail messages. Incoming mail messages is working but I can't reply. For some reason my internet provider technical support won't help me with my outgoing mail server settings & tell me to contact Apple. Do I check the box for "automatically manage connection settings"? Authentication is currently set on "none". The other authentication setting options are: External (TLS client certificate), Kerbos Version 5 (GSSAP1), NTLM, MD5 challenge response & password. Any suggestions is greatly appreciated.