The Mailer uses the system values for the connection.
You have a few options:
public void Send(SmtpMail message)
public void Send(SmtpMail message, IEnumerable<KeyValuePair<string, string>> attachments)
public void Send(SmtpMail message, IEnumerable<KeyValuePair<string, Stream>> attachments)
public void Send(SmtpMail message, IEnumerable<KeyValuePair<string, byte[]>> attachments)
You can set the from, to, etc in the SmtpMail object.
If you wanna peek yourself it lives in Epicor.Ice.Dll