diff --git a/components/email/email-composer.tsx b/components/email/email-composer.tsx
index 12314cb5..4d74944f 100644
--- a/components/email/email-composer.tsx
+++ b/components/email/email-composer.tsx
@@ -50,11 +50,15 @@ import {
 } from "@/lib/email-composer-utils";
 import { RichTextEditor } from "@/components/email/rich-text-editor";
 import type { Editor } from "@tiptap/react";
+import { htmlToPlainText as htmlToPlainTextShared } from "@/lib/html-to-text";
 
-/** Strip HTML tags and decode entities to get a plain-text version */
+/**
+ * Derives the text/plain alternative from the composer's HTML body, preserving
+ * line structure from block elements and <br> tags. Paragraph spacing is on so
+ * <p> blocks are separated by a blank line, matching their visual rendering (#421).
+ */
 function htmlToPlainText(html: string): string {
-  const doc = new DOMParser().parseFromString(html, 'text/html');
-  return doc.body.textContent || '';
+  return htmlToPlainTextShared(html, { paragraphSpacing: true });
 }
 
 /**
diff --git a/lib/__tests__/html-to-text.test.ts b/lib/__tests__/html-to-text.test.ts
new file mode 100644
index 00000000..4f3bcee2
--- /dev/null
+++ b/lib/__tests__/html-to-text.test.ts
@@ -0,0 +1,57 @@
+import { describe, expect, it } from 'vitest';
+
+import { htmlToPlainText } from '../html-to-text';
+
+describe('htmlToPlainText', () => {
+  it('preserves line breaks from <br> within a paragraph', () => {
+    expect(htmlToPlainText('<p>Line 1.<br>Line 2.</p>')).toBe('Line 1.\nLine 2.');
+  });
+
+  it('separates block elements with newlines instead of running them together (#421)', () => {
+    // The previous textContent-based implementation produced "Line 1.Line 2.Paragraph 2."
+    expect(htmlToPlainText('<div>Line 1.</div><div>Line 2.</div><div>Paragraph 2.</div>')).toBe(
+      'Line 1.\nLine 2.\nParagraph 2.'
+    );
+  });
+
+  it('with paragraphSpacing, separates paragraphs with a blank line', () => {
+    expect(
+      htmlToPlainText('<p>Line 1.<br>Line 2.</p><p>Paragraph 2.</p>', { paragraphSpacing: true })
+    ).toBe('Line 1.\nLine 2.\n\nParagraph 2.');
+  });
+
+  it('without paragraphSpacing, separates paragraphs with a single newline', () => {
+    expect(htmlToPlainText('<p>A</p><p>B</p>')).toBe('A\nB');
+  });
+
+  it('renders links as text when the text equals the href', () => {
+    expect(
+      htmlToPlainText('<p><a href="mailto:alice@example.com">alice@example.com</a></p>')
+    ).toBe('alice@example.com');
+  });
+
+  it('renders links as "text <href>" when they differ', () => {
+    expect(htmlToPlainText('<p>Visit <a href="https://example.com">our site</a></p>')).toBe(
+      'Visit our site <https://example.com>'
+    );
+  });
+
+  it('collapses excess whitespace and trims the result', () => {
+    expect(htmlToPlainText('  <p>  Hello   world  </p>  ')).toBe('Hello world');
+  });
+
+  it('caps consecutive blank lines at one', () => {
+    expect(htmlToPlainText('<p>A</p><br><br><br><p>B</p>', { paragraphSpacing: true })).toBe(
+      'A\n\nB'
+    );
+  });
+
+  it('returns an empty string for empty or whitespace-only HTML', () => {
+    expect(htmlToPlainText('')).toBe('');
+    expect(htmlToPlainText('   <p>  </p>  ')).toBe('');
+  });
+
+  it('handles nested lists as separate lines', () => {
+    expect(htmlToPlainText('<ul><li>One</li><li>Two</li></ul>')).toBe('One\nTwo');
+  });
+});
diff --git a/lib/html-to-text.ts b/lib/html-to-text.ts
new file mode 100644
index 00000000..941bbbcb
--- /dev/null
+++ b/lib/html-to-text.ts
@@ -0,0 +1,164 @@
+import { parseHtmlSafely } from '@/lib/email-sanitization';
+
+// Block-level tags whose boundaries become line breaks in the plain-text
+// rendering. Without this, the DOM's textContent would run every block
+// together on a single line (#421).
+const BLOCK_TAGS = new Set([
+  'address',
+  'article',
+  'aside',
+  'blockquote',
+  'div',
+  'dd',
+  'dl',
+  'dt',
+  'footer',
+  'h1',
+  'h2',
+  'h3',
+  'h4',
+  'h5',
+  'h6',
+  'header',
+  'li',
+  'nav',
+  'ol',
+  'p',
+  'pre',
+  'section',
+  'table',
+  'tr',
+  'ul',
+]);
+
+// Paragraph-level blocks that, with `paragraphSpacing` enabled, are separated by
+// a blank line rather than a single newline - matching how they render visually.
+const PARAGRAPH_TAGS = new Set([
+  'blockquote',
+  'h1',
+  'h2',
+  'h3',
+  'h4',
+  'h5',
+  'h6',
+  'ol',
+  'p',
+  'pre',
+  'table',
+  'ul',
+]);
+
+export interface HtmlToPlainTextOptions {
+  /**
+   * Separate paragraph-level blocks (<p>, headings, lists, ...) with a blank
+   * line instead of a single newline. Use for email bodies where paragraphs
+   * are visually spaced; leave off for compact output like signatures.
+   */
+  paragraphSpacing?: boolean;
+}
+
+function normalizeLineBreaks(value: string): string {
+  return value
+    .replace(/\r\n?/g, '\n')
+    .replace(new RegExp(String.fromCharCode(160), 'g'), ' ')
+    .replace(/[ \t]+\n/g, '\n')
+    .replace(/\n{3,}/g, '\n\n')
+    .trim();
+}
+
+/**
+ * Converts HTML into readable plain text, preserving line structure from block
+ * elements and <br> tags. Links render as `text <href>` unless the text already
+ * is the href. Used to derive the text/plain alternative of an HTML email.
+ */
+export function htmlToPlainText(html: string, options: HtmlToPlainTextOptions = {}): string {
+  const { paragraphSpacing = false } = options;
+  const document = parseHtmlSafely(html);
+  const chunks: string[] = [];
+
+  const appendText = (value: string) => {
+    if (!value) return;
+    const normalized = value.replace(/\s+/g, ' ');
+    if (!normalized.trim()) return;
+    const previous = chunks[chunks.length - 1];
+    if (previous && !previous.endsWith('\n') && !previous.endsWith(' ')) {
+      chunks.push(' ');
+    }
+    chunks.push(normalized);
+  };
+
+  // Number of newline characters already trailing the accumulated output.
+  const trailingNewlines = (): number => {
+    let count = 0;
+    for (let i = chunks.length - 1; i >= 0; i--) {
+      const chunk = chunks[i];
+      let j = chunk.length - 1;
+      let inner = 0;
+      while (j >= 0 && chunk[j] === '\n') {
+        inner++;
+        j--;
+      }
+      count += inner;
+      if (j >= 0) break; // chunk had non-newline content, stop counting
+    }
+    return count;
+  };
+
+  // Ensures at least `min` trailing newlines, without emitting leading ones.
+  const ensureNewlines = (min: number) => {
+    if (chunks.length === 0) return;
+    for (let current = trailingNewlines(); current < min; current++) {
+      chunks.push('\n');
+    }
+  };
+
+  const walk = (node: Node) => {
+    if (node.nodeType === Node.TEXT_NODE) {
+      appendText(node.textContent || '');
+      return;
+    }
+
+    if (node.nodeType !== Node.ELEMENT_NODE) {
+      return;
+    }
+
+    const element = node as HTMLElement;
+    const tagName = element.tagName.toLowerCase();
+
+    if (tagName === 'br') {
+      // Additive so consecutive <br> can form a blank line (capped by normalize).
+      if (chunks.length > 0) chunks.push('\n');
+      return;
+    }
+
+    if (tagName === 'a') {
+      const text = element.textContent?.replace(/\s+/g, ' ').trim() || '';
+      const href = element.getAttribute('href')?.trim() || '';
+      const normalizedHref = href.replace(/^mailto:/i, '');
+      if (text && normalizedHref && text === normalizedHref) {
+        appendText(text);
+        return;
+      }
+      if (text && href && text !== href) {
+        appendText(`${text} <${href}>`);
+        return;
+      }
+    }
+
+    const separator = paragraphSpacing && PARAGRAPH_TAGS.has(tagName) ? 2 : 1;
+    const isBlock = BLOCK_TAGS.has(tagName);
+
+    if (isBlock) {
+      ensureNewlines(separator);
+    }
+
+    Array.from(element.childNodes).forEach(walk);
+
+    if (isBlock) {
+      ensureNewlines(separator);
+    }
+  };
+
+  Array.from(document.body.childNodes).forEach(walk);
+  return normalizeLineBreaks(chunks.join(''));
+}
diff --git a/lib/signature-utils.ts b/lib/signature-utils.ts
index 678fa461..b707b49e 100644
--- a/lib/signature-utils.ts
+++ b/lib/signature-utils.ts
@@ -1,25 +1,11 @@
 import { parseHtmlSafely, sanitizeSignatureHtml } from '@/lib/email-sanitization';
+import { htmlToPlainText } from '@/lib/html-to-text';
 
 type SignatureSource = {
   textSignature?: string;
   htmlSignature?: string;
 };
 
-const BLOCK_TAGS = new Set([
-  'address',
-  'article',
-  'aside',
-  'blockquote',
-  'div',
-  'footer',
-  'header',
-  'li',
-  'nav',
-  'p',
-  'section',
-  'tr',
-]);
-
 function normalizeSignatureLineBreaks(value: string): string {
   return value
     .replace(/\r\n?/g, '\n')
@@ -29,75 +15,6 @@ function normalizeSignatureLineBreaks(value: string): string {
     .trim();
 }
 
-function htmlToPlainText(html: string): string {
-  const document = parseHtmlSafely(html);
-  const chunks: string[] = [];
-
-  const appendText = (value: string) => {
-    if (!value) return;
-    const normalized = value.replace(/\s+/g, ' ');
-    if (!normalized.trim()) return;
-    const previous = chunks[chunks.length - 1];
-    if (previous && !previous.endsWith('\n') && !previous.endsWith(' ')) {
-      chunks.push(' ');
-    }
-    chunks.push(normalized);
-  };
-
-  const appendNewline = () => {
-    const previous = chunks[chunks.length - 1];
-    if (previous === '\n') return;
-    if (previous?.endsWith('\n')) return;
-    chunks.push('\n');
-  };
-
-  const walk = (node: Node) => {
-    if (node.nodeType === Node.TEXT_NODE) {
-      appendText(node.textContent || '');
-      return;
-    }
-
-    if (node.nodeType !== Node.ELEMENT_NODE) {
-      return;
-    }
-
-    const element = node as HTMLElement;
-    const tagName = element.tagName.toLowerCase();
-
-    if (tagName === 'br') {
-      appendNewline();
-      return;
-    }
-
-    if (tagName === 'a') {
-      const text = element.textContent?.replace(/\s+/g, ' ').trim() || '';
-      const href = element.getAttribute('href')?.trim() || '';
-      const normalizedHref = href.replace(/^mailto:/i, '');
-      if (text && normalizedHref && text === normalizedHref) {
-        appendText(text);
-        return;
-      }
-      if (text && href && text !== href) {
-        appendText(`${text} <${href}>`);
-        return;
-      }
-    }
-
-    if (BLOCK_TAGS.has(tagName) && chunks.length > 0) {
-      appendNewline();
-    }
-
-    Array.from(element.childNodes).forEach(walk);
-
-    if (BLOCK_TAGS.has(tagName)) {
-      appendNewline();
-    }
-  };
-
-  Array.from(document.body.childNodes).forEach(walk);
-  return normalizeSignatureLineBreaks(chunks.join(''));
-}
-
 export function getPlainTextSignature(signature?: SignatureSource | null): string {
   if (signature?.textSignature?.trim()) {
     return normalizeSignatureLineBreaks(signature.textSignature);