diff --git a/api/src/email.ts b/api/src/email.ts
index 2832fe2..5dcda6a 100644
--- a/api/src/email.ts
+++ b/api/src/email.ts
@@ -34,6 +34,36 @@ function getTransporter(): nodemailer.Transporter {
   return _transporter;
 }
 
+// ─── HTML → plaintext (dependency-free) ─────────────────────────────────────
+// A multipart/alternative (which nodemailer builds when both html+text are
+// given) with ONLY an HTML part is malformed, and HTML-only mail is a spam
+// signal. When a caller doesn't supply `text`, derive a readable plaintext
+// fallback from the HTML so every message ships a proper text/plain part.
+export function htmlToText(html: string): string {
+  if (!html) return "";
+  let s = html;
+  // Drop non-content blocks entirely.
+  s = s.replace(/<(script|style|head)[\s\S]*?<\/\1>/gi, "");
+  // <a href="url">text</a>  ->  text (url)
+  s = s.replace(/<a\b[^>]*\bhref\s*=\s*["']?([^"'>\s]+)["']?[^>]*>([\s\S]*?)<\/a>/gi,
+    (_m, url, txt) => {
+      const t = txt.replace(/<[^>]+>/g, "").trim();
+      return t && !url.startsWith("mailto:") && t !== url ? `${t} (${url})` : (t || url);
+    });
+  // List items -> "- item"; block/line breaks -> newlines.
+  s = s.replace(/<li\b[^>]*>/gi, "\n- ");
+  s = s.replace(/<\/(p|div|tr|h[1-6]|li|ul|ol|table)>/gi, "\n");
+  s = s.replace(/<br\s*\/?>/gi, "\n");
+  // Strip remaining tags, unescape common entities, collapse whitespace.
+  s = s.replace(/<[^>]+>/g, "");
+  s = s.replace(/&nbsp;/gi, " ").replace(/&amp;/gi, "&").replace(/&lt;/gi, "<")
+       .replace(/&gt;/gi, ">").replace(/&quot;/gi, '"').replace(/&#39;/gi, "'")
+       .replace(/&rarr;/gi, "->").replace(/&middot;/gi, "-").replace(/&sect;/gi, "Section");
+  s = s.replace(/[ \t]+/g, " ").replace(/[ \t]+\n/g, "\n").replace(/\n{3,}/g, "\n\n");
+  s = s.split("\n").map((line) => line.trim()).join("\n");
+  return s.trim();
+}
+
 // ─── Generic send ─────────────────────────────────────────────────────────────
 
 export async function sendEmail(opts: { to: string; subject: string; html: string; text?: string; cc?: string }): Promise<void> {
@@ -44,7 +74,7 @@ export async function sendEmail(opts: { to: string; subject: string; html: strin
     ...(opts.cc ? { cc: opts.cc } : {}),
     subject: opts.subject,
     html: opts.html,
-    text: opts.text || "",
+    text: opts.text || htmlToText(opts.html),
   });
 }
 
diff --git a/scripts/formation/document_delivery.py b/scripts/formation/document_delivery.py
index 65b3d86..5480a9d 100644
--- a/scripts/formation/document_delivery.py
+++ b/scripts/formation/document_delivery.py
@@ -267,9 +267,13 @@ def _build_email(
     msg["Subject"] = f"Your {type_display} Has Been Filed — {entity_name}"
     msg["Reply-To"] = FROM_EMAIL
 
-    # HTML body
-    html_part = email.mime.text.MIMEText(html_body, "html", "utf-8")
-    msg.attach(html_part)
+    # HTML body wrapped in alternative with a plaintext sibling (HTML-only is
+    # malformed inside multipart + a spam signal); documents attach to mixed root.
+    from scripts._email_plaintext import html_to_text
+    alt = email.mime.multipart.MIMEMultipart("alternative")
+    alt.attach(email.mime.text.MIMEText(html_to_text(html_body), "plain", "utf-8"))
+    alt.attach(email.mime.text.MIMEText(html_body, "html", "utf-8"))
+    msg.attach(alt)
 
     # Attach documents
     for doc_path in documents:
diff --git a/scripts/workers/cdr_unlock_nudge.py b/scripts/workers/cdr_unlock_nudge.py
index 4d75c81..b24826f 100644
--- a/scripts/workers/cdr_unlock_nudge.py
+++ b/scripts/workers/cdr_unlock_nudge.py
@@ -23,6 +23,8 @@ from datetime import datetime, timedelta
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
 
+from scripts._email_plaintext import html_to_text
+
 import psycopg2
 import psycopg2.extras
 
@@ -81,6 +83,7 @@ def _send(to_email: str, subject: str, body_html: str) -> bool:
     msg["From"] = FROM_EMAIL
     msg["To"] = to_email
     msg["Bcc"] = ADMIN_EMAIL
+    msg.attach(MIMEText(html_to_text(body_html), "plain"))
     msg.attach(MIMEText(body_html, "html"))
     try:
         with smtplib.SMTP(SMTP_HOST, SMTP_PORT) as server:
diff --git a/scripts/workers/commission_worker.py b/scripts/workers/commission_worker.py
index 2c6b58d..25b3097 100644
--- a/scripts/workers/commission_worker.py
+++ b/scripts/workers/commission_worker.py
@@ -26,6 +26,8 @@ from collections import defaultdict
 from datetime import datetime, timedelta, timezone
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
+
+from scripts._email_plaintext import html_to_text
 from typing import Any
 
 import psycopg2
@@ -114,6 +116,7 @@ def _send_email(to: str, subject: str, body_html: str) -> None:
     msg["From"] = FROM_EMAIL
     msg["To"] = to
     msg["Subject"] = subject
+    msg.attach(MIMEText(html_to_text(body_html), "plain"))
     msg.attach(MIMEText(body_html, "html"))
 
     try:
diff --git a/scripts/workers/completion_emails.py b/scripts/workers/completion_emails.py
index e911c17..6923ab8 100644
--- a/scripts/workers/completion_emails.py
+++ b/scripts/workers/completion_emails.py
@@ -18,6 +18,8 @@ from datetime import datetime, timedelta, timezone
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
 
+from scripts._email_plaintext import html_to_text
+
 import psycopg2
 
 LOG = logging.getLogger("workers.completion_emails")
@@ -37,6 +39,7 @@ def send_email(to: str, subject: str, html: str):
     msg["From"] = f"Performance West <{SMTP_FROM}>"
     msg["To"] = to
     msg["Subject"] = subject
+    msg.attach(MIMEText(html_to_text(html), "plain"))
     msg.attach(MIMEText(html, "html"))
 
     import os as _smtp_os
diff --git a/scripts/workers/delivery_worker.py b/scripts/workers/delivery_worker.py
index afd5dc8..8c95ca4 100644
--- a/scripts/workers/delivery_worker.py
+++ b/scripts/workers/delivery_worker.py
@@ -354,10 +354,13 @@ def _send_email(to_address: str, subject: str, html_body: str) -> None:
     from email.mime.multipart import MIMEMultipart
     from email.mime.text import MIMEText
 
+    from scripts._email_plaintext import html_to_text
+
     msg = MIMEMultipart("alternative")
     msg["Subject"] = subject
     msg["From"] = SMTP_FROM
     msg["To"] = to_address
+    msg.attach(MIMEText(html_to_text(html_body), "plain"))
     msg.attach(MIMEText(html_body, "html"))
 
     with smtplib.SMTP(SMTP_HOST, SMTP_PORT) as server:
diff --git a/scripts/workers/intake_reminder.py b/scripts/workers/intake_reminder.py
index 19995b5..4431066 100644
--- a/scripts/workers/intake_reminder.py
+++ b/scripts/workers/intake_reminder.py
@@ -52,6 +52,8 @@ from datetime import datetime, timezone
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
 
+from scripts._email_plaintext import html_to_text
+
 import psycopg2
 import psycopg2.extras
 
@@ -112,6 +114,7 @@ def _send_email(to: str, subject: str, html: str) -> bool:
         msg["From"] = SMTP_FROM
         msg["To"] = to
         msg["Subject"] = subject
+        msg.attach(MIMEText(html_to_text(html), "plain"))
         msg.attach(MIMEText(html, "html"))
         with smtplib.SMTP(SMTP_HOST, SMTP_PORT, timeout=30) as s:
             s.starttls()
diff --git a/scripts/workers/job_server.py b/scripts/workers/job_server.py
index 03d37ae..8341eed 100644
--- a/scripts/workers/job_server.py
+++ b/scripts/workers/job_server.py
@@ -930,7 +930,13 @@ def _send_instant_delivery(
         f"Your {service_name} documents are ready \u2014 Order {order_number}"
     )
     msg["Reply-To"] = "info@performancewest.net"
-    msg.attach(MIMEText(html, "html"))
+    # text+html in an alternative sub-part (HTML-only is malformed/spam-signal),
+    # then PDFs/DOCX attach to the mixed root below.
+    from scripts._email_plaintext import html_to_text
+    alt = MIMEMultipart("alternative")
+    alt.attach(MIMEText(html_to_text(html), "plain"))
+    alt.attach(MIMEText(html, "html"))
+    msg.attach(alt)
 
     # Download deliverables from MinIO and attach (PDF + DOCX)
     with tempfile.TemporaryDirectory() as tmpdir:
@@ -1020,7 +1026,12 @@ def _send_filing_confirmation(
     msg["To"] = customer_email
     msg["Subject"] = f"\u2705 Filed: {service_name} \u2014 Confirmation {confirmation_number}"
     msg["Reply-To"] = "info@performancewest.net"
-    msg.attach(MIMEText(html, "html"))
+    # text+html in an alternative sub-part (HTML-only is malformed/spam-signal).
+    from scripts._email_plaintext import html_to_text
+    alt = MIMEMultipart("alternative")
+    alt.attach(MIMEText(html_to_text(html), "plain"))
+    alt.attach(MIMEText(html, "html"))
+    msg.attach(alt)
 
     # Attach confirmation PDFs
     pdf_paths = [p for p in minio_paths if p.lower().endswith(".pdf")]
diff --git a/scripts/workers/quarterly_499q_notify.py b/scripts/workers/quarterly_499q_notify.py
index e5709ad..0a44fc1 100644
--- a/scripts/workers/quarterly_499q_notify.py
+++ b/scripts/workers/quarterly_499q_notify.py
@@ -29,6 +29,8 @@ from datetime import date, timedelta
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
 
+from scripts._email_plaintext import html_to_text
+
 import psycopg2
 import psycopg2.extras
 
@@ -48,6 +50,7 @@ def _send_email(to: str, subject: str, html: str) -> bool:
         msg["From"] = SMTP_FROM
         msg["To"] = to
         msg["Subject"] = subject
+        msg.attach(MIMEText(html_to_text(html), "plain"))
         msg.attach(MIMEText(html, "html"))
         with smtplib.SMTP(SMTP_HOST, SMTP_PORT, timeout=30) as s:
             s.starttls()
diff --git a/scripts/workers/renewal_worker.py b/scripts/workers/renewal_worker.py
index 83ccd6b..b681f9b 100644
--- a/scripts/workers/renewal_worker.py
+++ b/scripts/workers/renewal_worker.py
@@ -60,11 +60,14 @@ def send_email(to_email: str, subject: str, html_body: str):
     from email.mime.multipart import MIMEMultipart
     from email.mime.text import MIMEText
 
+    from scripts._email_plaintext import html_to_text
+
     smtp_cfg = get_smtp_config()
     msg = MIMEMultipart("alternative")
     msg["From"] = f"Performance West <{smtp_cfg['from_addr']}>"
     msg["To"] = to_email
     msg["Subject"] = subject
+    msg.attach(MIMEText(html_to_text(html_body), "plain"))
     msg.attach(MIMEText(html_body, "html"))
 
     with smtplib.SMTP(smtp_cfg["host"], smtp_cfg["port"]) as server:
diff --git a/scripts/workers/services/base_handler.py b/scripts/workers/services/base_handler.py
index a76f7b6..69a5021 100644
--- a/scripts/workers/services/base_handler.py
+++ b/scripts/workers/services/base_handler.py
@@ -282,6 +282,8 @@ class BaseServiceHandler(ABC):
                 from email.mime.text import MIMEText
                 from email.mime.multipart import MIMEMultipart
 
+                from scripts._email_plaintext import html_to_text
+
                 first_name = customer_name.split(" ")[0] if customer_name else "there"
                 subject = f"Action Required — Complete your {service_label} intake"
                 body = (
@@ -308,6 +310,7 @@ class BaseServiceHandler(ABC):
                     msg["From"] = smtp_from
                     msg["To"] = customer_email
                     msg["Reply-To"] = "info@performancewest.net"
+                    msg.attach(MIMEText(html_to_text(body), "plain"))
                     msg.attach(MIMEText(body, "html"))
                     with smtplib.SMTP(smtp_host, smtp_port) as server:
                         server.starttls()
diff --git a/scripts/workers/services/fcc_carrier_registration.py b/scripts/workers/services/fcc_carrier_registration.py
index c4b2d0a..958e3f7 100644
--- a/scripts/workers/services/fcc_carrier_registration.py
+++ b/scripts/workers/services/fcc_carrier_registration.py
@@ -282,6 +282,8 @@ class FCCCarrierRegistrationHandler:
             from email.mime.text import MIMEText
             from email.mime.multipart import MIMEMultipart
 
+            from scripts._email_plaintext import html_to_text
+
             email = order.get("customer_email", "")
             name = order.get("customer_name", "")
             if not email:
@@ -302,6 +304,7 @@ class FCCCarrierRegistrationHandler:
             msg["Subject"] = subject
             msg["From"] = os.environ.get("SMTP_FROM", "Performance West <noreply@performancewest.net>")
             msg["To"] = email
+            msg.attach(MIMEText(html_to_text(body), "plain"))
             msg.attach(MIMEText(body, "html"))
 
             smtp_host = os.environ.get("SMTP_HOST", "co.carrierone.com")
diff --git a/scripts/workers/services/form_499a_discontinuance.py b/scripts/workers/services/form_499a_discontinuance.py
index 2d4320c..9feb44a 100644
--- a/scripts/workers/services/form_499a_discontinuance.py
+++ b/scripts/workers/services/form_499a_discontinuance.py
@@ -241,6 +241,8 @@ class Form499ADiscontinuanceHandler(BaseServiceHandler):
             from email.mime.multipart import MIMEMultipart
             from email.mime.text import MIMEText
 
+            from scripts._email_plaintext import html_to_text
+
             subject = f"Form 499-A Discontinuance Filed — {entity_name}"
             html = f"""
             <div style="font-family:Inter,sans-serif;max-width:600px;margin:0 auto;color:#1f2937">
@@ -275,6 +277,7 @@ class Form499ADiscontinuanceHandler(BaseServiceHandler):
             msg["From"] = os.environ.get("SMTP_FROM", "Performance West <noreply@performancewest.net>")
             msg["To"] = to
             msg["Subject"] = subject
+            msg.attach(MIMEText(html_to_text(html), "plain"))
             msg.attach(MIMEText(html, "html"))
 
             with smtplib.SMTP(
diff --git a/scripts/workers/services/form_499q.py b/scripts/workers/services/form_499q.py
index 90b7326..4e83d9a 100644
--- a/scripts/workers/services/form_499q.py
+++ b/scripts/workers/services/form_499q.py
@@ -338,10 +338,13 @@ class Form499QHandler(BaseServiceHandler):
             from email.mime.multipart import MIMEMultipart
             from email.mime.text import MIMEText
 
+            from scripts._email_plaintext import html_to_text
+
             msg = MIMEMultipart("alternative")
             msg["From"] = os.environ.get("SMTP_FROM", "Performance West <noreply@performancewest.net>")
             msg["To"] = to
             msg["Subject"] = subject
+            msg.attach(MIMEText(html_to_text(html), "plain"))
             msg.attach(MIMEText(html, "html"))
 
             with smtplib.SMTP(
diff --git a/scripts/workers/services/rmd_filing.py b/scripts/workers/services/rmd_filing.py
index f0f13cf..c278093 100644
--- a/scripts/workers/services/rmd_filing.py
+++ b/scripts/workers/services/rmd_filing.py
@@ -136,6 +136,8 @@ class RMDFilingHandler(BaseServiceHandler):
                     import smtplib
                     from email.mime.text import MIMEText
                     from email.mime.multipart import MIMEMultipart
+
+                    from scripts._email_plaintext import html_to_text
                     subject = f"Action Required — Review your RMD certification for {entity.get('legal_name', order_number)}"
                     body = (
                         f"<h2>Your RMD Certification is Ready for Review</h2>"
@@ -161,6 +163,7 @@ class RMDFilingHandler(BaseServiceHandler):
                         msg["From"] = smtp_from
                         msg["To"] = customer_email
                         msg["Reply-To"] = "info@performancewest.net"
+                        msg.attach(MIMEText(html_to_text(body), "plain"))
                         msg.attach(MIMEText(body, "html"))
                         with smtplib.SMTP(smtp_host, smtp_port) as server:
                             server.starttls()
diff --git a/scripts/workers/services/telecom/auto_filing.py b/scripts/workers/services/telecom/auto_filing.py
index f6145de..4acb9fc 100644
--- a/scripts/workers/services/telecom/auto_filing.py
+++ b/scripts/workers/services/telecom/auto_filing.py
@@ -44,6 +44,8 @@ import smtplib
 from dataclasses import dataclass
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
+
+from scripts._email_plaintext import html_to_text
 from typing import Optional
 
 logger = logging.getLogger(__name__)
@@ -279,6 +281,7 @@ def _send_admin_email(
     msg["Subject"] = f"[Review & File] {order_number} — {service_name}"
     msg["From"] = smtp_from
     msg["To"] = to_email
+    msg.attach(MIMEText(html_to_text(html), "plain"))
     msg.attach(MIMEText(html, "html"))
 
     try:
diff --git a/scripts/workers/services/telecom/esign_helper.py b/scripts/workers/services/telecom/esign_helper.py
index eda6b6a..5b3a1b4 100644
--- a/scripts/workers/services/telecom/esign_helper.py
+++ b/scripts/workers/services/telecom/esign_helper.py
@@ -28,6 +28,8 @@ import smtplib
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
 
+from scripts._email_plaintext import html_to_text
+
 logger = logging.getLogger("esign_helper")
 
 
@@ -197,6 +199,7 @@ def _send_signing_email(
     msg["To"] = f"{to_name} <{to_email}>"
     msg["Subject"] = subject
     msg["Reply-To"] = "info@performancewest.net"
+    msg.attach(MIMEText(html_to_text(body), "plain"))
     msg.attach(MIMEText(body, "html"))
 
     with smtplib.SMTP(smtp_host, smtp_port, timeout=30) as server:
diff --git a/scripts/workers/usf_factor_monitor.py b/scripts/workers/usf_factor_monitor.py
index 4d7e33b..db93869 100644
--- a/scripts/workers/usf_factor_monitor.py
+++ b/scripts/workers/usf_factor_monitor.py
@@ -52,6 +52,8 @@ from datetime import date, datetime
 from decimal import Decimal, InvalidOperation
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
+
+from scripts._email_plaintext import html_to_text
 from typing import Iterable
 
 import psycopg2
@@ -604,6 +606,7 @@ def send_email(*, to_email: str, subject: str, html_body: str, dry_run: bool) ->
     msg["From"] = FROM_EMAIL
     msg["To"] = to_email
     msg["Bcc"] = ADMIN_EMAIL
+    msg.attach(MIMEText(html_to_text(html_body), "plain"))
     msg.attach(MIMEText(html_body, "html"))
     try:
         with smtplib.SMTP(SMTP_HOST, SMTP_PORT) as server:
diff --git a/scripts/workers/worker_email.py b/scripts/workers/worker_email.py
index 58cdbc4..ad5d629 100644
--- a/scripts/workers/worker_email.py
+++ b/scripts/workers/worker_email.py
@@ -17,10 +17,21 @@ from __future__ import annotations
 import logging
 import os
 import smtplib
+import sys
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
 from email.mime.application import MIMEApplication
 
+# Shared HTML -> plaintext converter (scripts/_email_plaintext.py). Adding a
+# text/plain part to every message is a deliverability win: a multipart/
+# alternative with ONLY an HTML part is malformed, and HTML-only mail is a
+# spam-score signal. Import is path-tolerant (module run from /app or scripts/).
+try:
+    from scripts._email_plaintext import html_to_text
+except ImportError:  # pragma: no cover - fallback when scripts/ is on sys.path
+    sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+    from _email_plaintext import html_to_text  # type: ignore
+
 LOG = logging.getLogger("workers.email")
 
 SMTP_HOST = os.getenv("SMTP_HOST", "co.carrierone.com")
@@ -53,8 +64,13 @@ def send_worker_email(
         msg["Subject"] = subject
 
         alt = MIMEMultipart("alternative")
-        if text:
-            alt.attach(MIMEText(text, "plain"))
+        # Always include a text/plain part. If the caller did not supply one,
+        # derive it from the HTML so the message is a well-formed multipart/
+        # alternative (HTML-only is malformed + a spam signal). RFC 2046: list
+        # the plain part first (least->most preferred).
+        plain = text if text else html_to_text(html)
+        if plain:
+            alt.attach(MIMEText(plain, "plain"))
         alt.attach(MIMEText(html, "html"))
         msg.attach(alt)