As you probably know, one of the most popular MAILCast feature is the capabability to upload your sending in a ZIP archive (as shown in this article), because most of our customers still feel more comfortable editing their email within a desktop software than within an online one. But the matter is that buying an Adobe Dreamweaver or Microsoft Expression license just for this small task may be too expensive, so the solution are the multiple free html editors available into the internet.
These are some of the ones that we recommend to you:
Kompozer
KompoZer is a complete web authoring system based on NVU that combines web file management and easy-to-use WYSIWYG web page editing.
Aptana
Aptana Studio is a free complete web development environment based on Eclipse that combines powerful authoring tools with a collection of online hosting and collaboration services.
Amaya
Amaya is an open source Web editor hosted by W3C. The Amaya software is available for Windows, Unix platforms and MacOS X.