Module smtplib Has No Attribute SMTP

This is a Python error, not an SMTP server response. The 3-digit SMTP reply codes in RFC 5321 (and the enhanced codes in RFC 3463) come from a mail server; this AttributeError is raised by the Python interpreter before any network connection is made. So nothing here is a deliverability, auth, or TLS problem — it's a module-resolution problem in your own project.

What causes "module 'smtplib' has no attribute 'SMTP'"?

Python's smtplib standard-library module exposes SMTP, SMTP_SSL, and LMTP classes (Python docs). If smtplib.SMTP suddenly "doesn't exist," Python is almost certainly importing the wrong smtplib — yours, not the standard library's.

The usual trigger is name shadowing. When you run import smtplib, the interpreter searches built-in modules, then the current directory, then the rest of sys.path. If you have a file named smtplib.py (or a package folder smtplib/) sitting next to your script, your file wins the lookup. Your file doesn't define an SMTP class, so smtplib.SMTP(...) fails.

A file named email.py breaks the import differently: because stdlib smtplib does import email.utils internally, a local email.py shadow makes Python fail while importing smtplib itself, raising ModuleNotFoundError: No module named 'email.utils'; 'email' is not a package — not the AttributeError this page is about, but the same root cause (a shadowing file) and the same fix.

A stale compiled cache is sometimes blamed for this sticking around after a fix, but in practice it's rarely the culprit: once you rename or delete the shadowing file, Python resolves smtplib back to the standard library on the next run.

How do I fix "module 'smtplib' has no attribute 'SMTP'"?

1. Find the shadowing file. Add this above your import and run the script:

import smtplib
print(smtplib.__file__)

If it prints a path inside your project (e.g. /your/project/smtplib.py) instead of your Python install's .../lib/python3.x/smtplib.py, that file is the culprit. email.py and smtp.py shadow things the same way.

2. Rename it to something that isn't a standard-library name, e.g. mailer.py or send_email.py, and update any imports that referenced the old name.

3. As a safety measure, clear any stale bytecode, though in practice renaming/deleting the shadowing file alone is normally sufficient — CPython will not keep resolving to a deleted module's stale bytecode under the fixed name:

find . -name '__pycache__' -type d -prune -exec rm -rf {} +
find . -name '*.pyc' -delete

4. Re-run. smtplib.__file__ should now point at the standard library, and smtplib.SMTP("smtp.example.com", 587) will resolve.

If you can't find a shadowing file, run dir(smtplib) — if SMTP is missing from the list, you're still importing the wrong module; if it's present, recheck your line for a typo such as lowercase smtplib.smtp (the class is uppercase SMTP).

Correct usage once it's fixed

import smtplib
from email.message import EmailMessage

msg = EmailMessage()
msg["From"] = "you@example.com"
msg["To"] = "user@example.com"
msg["Subject"] = "Hello"
msg.set_content("Sent from Python")

with smtplib.SMTP("smtp.example.com", 587) as server:
    server.starttls()
    server.login("you@example.com", "your-app-password")
    server.send_message(msg)

Port 587 (STARTTLS) and 465 (implicit TLS via smtplib.SMTP_SSL) are both valid per RFC 8314. For Gmail, authenticate with an App Password (requires 2-Step Verification) or OAuth2 — Google removed Less Secure Apps access for personal Google accounts in May 2022. Google Workspace accounts followed a separate, later timeline, with basic-auth/LSA access fully cut off by May 1, 2025. None of this matters, though, until the import resolves to the real smtplib.