To send HTML messages from our announcement list system the images would have to be hosted on a web server somewhere so they could be linked to within the email message. You cannot paste in the raw MIME. Sending the images as attachments is generally a bad idea because it imposes all the extra bandwidth on the recipient of the newsletter whether they want it or not.
However, it is much easier for a relatively unskilled person to send the newsletter with the images as attachments. I agree with you there.
For a relatively small list, our discussion list Mailman system is generally ok to use for announcement type lists. Larger lists do not work especially well within our Mailman framework because they can slow down other email delivery. I don't know how large your lists is, but Mailman can probably easily handle lists up to maybe 1000 recipients. We officially don't support it and discourage it, but if our own announcement list system does not meet your technical requirements you can use the discussion list system.
Note that you must read and follow our spam policy with any bulk email. We have fairly strict guidelines designed to protect you from any complaints as well as protect our network from being blocked. You can see that here:
I encourage you to consider thinking of a way to enable your non-technical users to send these announcements without attaching all of the images. Attaching the images is sort of bad Internet etiquette as it forces every recipient to download the images no matter what connection they are using and whether they want to or not.
- DreamHost Head Honcho/Founder