My apologies for not being more direct with the instructions. The mail object settings are edited in the Universal Email interface with the envelope icon. In here you can configure what is the SMTP server and other details. This is where you would put in the authentication if it is needed, however this authentication only works for PEAR mail. If you are using regular mail then you should not need to enter any credentials. You mentioned:
"my host requires me to pass it a valid host name and user account on the mail server. It is plain PHP mail()"
This statement is a little confusing to me. From what I understand the standard php mail() does not support authentication. If you mean that you need to set the from parameter then this is configurable within the mail object settings by checking the box. It will use your from address for this, so make sure that you enter your appropriate email address for the from. Let us know if you have any further issues with this.