building my newsletter in #ProcessWire with the #ProMailer module has been great. Here is the custom interface I built for drafting dispatches. Notice there is also a #TiddlyWiki Import tab at the top, which accepts individual tiddler urls and will pull in the images and text from my wiki to help me get started with the draft.

The layout is also custom, down to the height of the body field and the placement of the columns and image fields.