diff --git a/.vscode/tasks.json b/.vscode/tasks.json
index 4bd0b99363..8b36b0e6ac 100644
--- a/.vscode/tasks.json
+++ b/.vscode/tasks.json
@@ -105,10 +105,11 @@
             "command": "/usr/local/bin/python",
             "args": [
                 "-m",
-                "smtpd",
+                "aiosmtpd",
                 "-n",
                 "-c",
-                "DebuggingServer",
+                "ietf.utils.aiosmtpd.DevDebuggingHandler",
+                "-l",
                 "localhost:2025"
             ],
             "presentation": {
diff --git a/docker/scripts/app-init.sh b/docker/scripts/app-init.sh
index 17e0c6c764..1d895cdf53 100755
--- a/docker/scripts/app-init.sh
+++ b/docker/scripts/app-init.sh
@@ -108,7 +108,7 @@ echo "Running initial checks..."
 
 if [ -z "$EDITOR_VSCODE" ]; then
     CODE=0
-    python -m smtpd -n -c DebuggingServer localhost:2025 &
+    python -m aiosmtpd -n -c ietf.utils.aiosmtpd.DevDebuggingHandler -l localhost:2025 &
     if [ -z "$*" ]; then
         echo "-----------------------------------------------------------------"
         echo "Ready!"
diff --git a/ietf/utils/test_smtpserver.py b/ietf/utils/aiosmtpd.py
similarity index 72%
rename from ietf/utils/test_smtpserver.py
rename to ietf/utils/aiosmtpd.py
index 40da758d66..3e4cd65dd9 100644
--- a/ietf/utils/test_smtpserver.py
+++ b/ietf/utils/aiosmtpd.py
@@ -1,10 +1,14 @@
 # Copyright The IETF Trust 2014-2025, All Rights Reserved
-# -*- coding: utf-8 -*-
+"""aiosmtpd-related utilities
 
+These are for testing / dev use. If you're using this for production code, think very
+hard about the choices you're making...
+"""
+from aiosmtpd import handlers
 from aiosmtpd.controller import Controller
 from aiosmtpd.smtp import SMTP
 from email.utils import parseaddr
-from typing import Optional
+from typing import Optional, TextIO
 
 
 class SMTPTestHandler:
@@ -54,3 +58,16 @@ def start(self):
 
     def stop(self):
         self.controller.stop()
+
+
+class DevDebuggingHandler(handlers.Debugging):
+    """Debugging handler for use in dev ONLY"""
+    def __init__(self, stream: Optional[TextIO] = None):
+        # Allow longer lines than the 1001 that RFC 5321 requires. As of 2025-04-16 the
+        # datatracker emits some non-compliant messages.
+        # See https://aiosmtpd.aio-libs.org/en/latest/smtp.html
+        # Doing this in a handler class is a huge hack. Tests all pass with this set
+        # to 4000, but make the limit longer for dev just in case.
+        SMTP.line_length_limit = 10000
+        super().__init__(stream)
+        
diff --git a/ietf/utils/test_runner.py b/ietf/utils/test_runner.py
index 08e81fd15c..1a3d4e5c3d 100644
--- a/ietf/utils/test_runner.py
+++ b/ietf/utils/test_runner.py
@@ -82,7 +82,7 @@
 import ietf
 import ietf.utils.mail
 from ietf.utils.management.commands import pyflakes
-from ietf.utils.test_smtpserver import SMTPTestServerDriver
+from ietf.utils.aiosmtpd import SMTPTestServerDriver
 from ietf.utils.test_utils import TestCase
 
 from mypy_boto3_s3.service_resource import Bucket