No.
You need to remember that RSS specification is a bit old. Adding images come development of RSS readers and not the specification for this format. This is where other formats come forward. Also, you don’t know how people are using RSS and how they building websites. This is outside of Hugo. Hugo provides base template for RSS and than you need to adjust it to your needs.
Yes, thats the point. You got here option to choose to serve whole content (.Content) or summary (.Summary). Hugo gives you flexability to adjust what you want to display.
From my example above I am taking a summary and, if featured image is available, adding featured image on front of summary.
Instead featured image (for example, if is not specified, you can grab first image from the post and add it. Like I am grabbing images in my post regarding adding image sitemap.
This is searching for images in content
{{ if (findRE `(?s)<img.+?>` .Content) }}{{ range $k, $_ := findRE `(?s)<img.+?>` .Content }}{{ if $k }}{{ end }}
And this is pasting link to images from <img src=
{{ replaceRE `(?s).*src="(.+?)".*` "$1" . | absURL }}
Than need to figure out how to pict first one and paste instead featured image:
{{ printf "<img src=\"%s\" />" $ftimgsrc.Permalink | safeHTML }}
from above code. Unable to help you more.
Remember, image is not shipped if you not specify in code that it need to be shipped.
This part from your original RSS file will output in HTML with all images.
<description>{{ .Content | html }}</description>
Read specification of each mail services (if available) to see what elements from RSS template they read and they use. I used to use TinyLetter (before it was sent to dir) with RSS and I managed to get what I want, but sometimes it was a struggle, as this service not always read the correct part of RSS field.