TEXT Email and HTML Email.. how merge and how appear in customer what his email clien

how in email design :
If I have two layouts of email TEXT Email and HTML Email… how merge and how appear in customer what his email client supports?

use multipart/alternative and create two separate sections in the email.

if the HTML part needs to contain any images then they can be attached using multipart/related and then they will only show up in the HTML

you use multipart/mixed to attach files that both versions can see

use multipart/alternative
using multipart/related
use multipart/mixed

What are these? can you provide sample code or web ref to an article with code include?

please also…
Also If I have a newsletter in html single page form, how to send it?
I know PHP send emails and attachments, but exist easier way…?
I have GMAIL, OUTLOOK 2010, 2003, YAHOO MAIL, HOTMAIL.