Exercise: Send plain text e-mail.

Create a function that will get one or more addresses where To send the message, 0 or more address to Cc the message. A single addres to pretend as the From field.

Get a string to be the Subject line and some plain text to be the body of the e-mail.

By default this should assume to be running on a Linux/Unix system with a properly configured sendmail program and use that as the underlying transporting system.

Then also add an optional parameter SMTP that holds the name or IP address of an SMTP server. When this parameter is given, use the SMTP server to send the e-mail.