If I use HTML in e-mails, I usually want just some
blockquote tags, nothing else. If I compose a HTML e-mail in any of the e-mail clients I know, it probably adds some
br tags and I want to avoid those. A similarly bad thing is that the tags are invisible and it is hard to check the formatting and if there are some unwanted tags.
I imagine that the e-mail client could work in one of the following ways. The first is that I could edit the HTML directly. The second is that I could write the e-mail in a simple markup, like Markdown, and it would be converted to HTML while being sent. The third is that the e-mail compositor would be WYSIWYG and would have a clean-HTML mode, where it would use only a configurable limited subset of HTML.
I know that I could write a script using some CLI tools to send these e-mails, but I want something with a nice GUI, that I could use as my main e-mail client. Also, the software should work on Linux because that is what I use.