On a related note, while I love the UX of mutt, I do find proportional fonts to be significantly more readable than fixed-width fonts for paragraphs of natural-language text.
Given the near ubiquitous use of top-posting and quoting the entire message that's being replied to, it stands to reason that others are not really reading the quoted material and are just reading the response on top.
> and the inability to have inline images
I wonder when email clients like Outlook would start rendering images based on a URL included in the message, similar to what Slack does. That could allow one to effectively include an inline image, which would be seen as a URL in other clients.
Given the proliferation of rendering a thread of messages and showing them as a conversation (i.e., conversation view), reading the quoted material within the same message is not really necessary.
> Technical (and also nontechnical) exchanges often consist of a dozen messages about a particular topic spread over weeks or sometimes months, where at almost each step you want to go back in the conversation to look at details of the previous discussion or to refresh your memory.
While I have seen this done in threads where people follow the conventions of a typical mailing list or usenet newsgroup by replying inline and quoting only parts of the text they're responding to, I have not seen the equivalent in a threaded conversation in outlook. And, as you note:
> Outlook also doesn't have a great UX for that.
While they have addressed the UX issue to some extent with the conversation view, it still doesn't really lend itself to easily following the discussion amongst multiple people due to the fact that they don't typically use different subthreads under the same email chain.
For sending emails with formatting (italics, headings), I use Markdown in Vim then press H in Mutt before sending, which pipes it through an appropriate filter:
set send_multipart_alternative_filter=html_alternative send-hook . 'set send_multipart_alternative=no' macro compose H ':set send_multipart_alternative=yes<Enter><view-alt-mailcap>' 'add HTML alternative'