OT: How to send email that is both text-only and/or html?

[Josef Lowder]

.
Is there a way to send an email message that is both text-only
and/or html?  While I totally agree with keeping most email
text only, and I very rarely use html ... it is nice to send a
Christmas letter with embedded photos, and some nice holiday
graphics.  So what would be the best way to do that and still
have a text-only version delivered to friends and family with
dial-up only connections for whom emails with lots of photos
might be a problem?