diff --git a/lib/base_markdown_renderer.rb b/lib/base_markdown_renderer.rb
index df49918b3..f530e71ee 100644
--- a/lib/base_markdown_renderer.rb
+++ b/lib/base_markdown_renderer.rb
@@ -29,11 +29,15 @@ class BaseMarkdownRenderer < CommonMarker::HtmlRenderer
 
   def render_img_tag(src, title, height = nil)
     title_attribute = title.present? ? " title=\"#{title}\"" : ''
-    height_attribute = height ? " height=\"#{height}\" width=\"auto\"" : ''
+    # Use inline style instead of the HTML height attribute: email clients and
+    # the in-app Letter view both run images through CSS (e.g. prose /
+    # lettersanitizer's `img { height: auto }`) which overrides presentational
+    # attributes. Inline style has higher specificity and survives.
+    style_attribute = height ? " style=\"height: #{height};\"" : ''
 
     plain do
       # plain ensures that the content is not wrapped in a paragraph tag
-      out("<img src=\"#{src}\"#{title_attribute}#{height_attribute} />")
+      out("<img src=\"#{src}\"#{title_attribute}#{style_attribute} />")
     end
   end
 end
diff --git a/spec/lib/base_markdown_renderer_spec.rb b/spec/lib/base_markdown_renderer_spec.rb
index 262e78daf..f8bdae4be 100644
--- a/spec/lib/base_markdown_renderer_spec.rb
+++ b/spec/lib/base_markdown_renderer_spec.rb
@@ -12,7 +12,7 @@ describe BaseMarkdownRenderer do
     context 'when image has a height' do
       it 'renders the img tag with the correct attributes' do
         markdown = '![Sample Title](https://example.com/image.jpg?cw_image_height=100)'
-        expect(render_markdown(markdown)).to include('<img src="https://example.com/image.jpg?cw_image_height=100" height="100" width="auto" />')
+        expect(render_markdown(markdown)).to include('<img src="https://example.com/image.jpg?cw_image_height=100" style="height: 100;" />')
       end
     end