Telling anyone to avoid HTML e-mail at this point in history (and by avoid I don't mean changing how one might choose to view messages) is an exercise in futility, to put it mildly.  It can also result in a major loss of content and actual ease of access from many e-mail messages.

HTML format has been the de facto convention for a very long time now.  Most screen readers seem to do quite well with it, in my observation, and they'd have to since the vast majority of e-mail messages these days involve HTML formatting.

The HTML ship has sailed and the days of the plain-text dinghy are never coming back - at least if one wishes to conform oneself to the wider world as it is.
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Brian - Windows 10 Pro, 64-Bit, Version 1909, Build 18363  

Most of the change we think we see in life is due to truths being in and out of favor.

         ~ Robert Frost, The Black Cottage (1914)