If you searched for "python send email smtp", "send email python", or "smtplib python", the production-safe path is: 1. build messages with `EmailMessage` 2. send with `smtplib` using explicit TLS and authentication 3. keep SMTP settings in environment variables 4. verify inbox receipt, links, HTML, and attachments before release Python can send a message in a few lines, but production email needs more than a successful `send_message()` call. You need to know that the email arrived, rendered correctly, and contained the expected links, codes, headers, and attachments. ![python smtp](/assets/python-smtp.jpg) ## Choose the right Python email path | Need | Recommended path | Why | | --------------------------------------------- | ------------------------------------------ | ------------------------------------------------------------- | | Learn the SMTP basics | `smtplib` with a plain text message | Smallest standard-library example. | | Send transactional app email | `EmailMessage` plus authenticated SMTP | Handles headers, MIME, HTML, and attachments cleanly. | | Run CI checks for signup, reset, or OTP email | MailSlurp inbox plus wait-for-email checks | Confirms the email actually arrived and matched expectations. | | Prefer API-first sending | MailSlurp API or SDK | Easier to log, retry, and assert in automated workflows. | If you are deciding between SMTP and an HTTP email API, compare the tradeoffs in [SMTP vs HTTP email APIs](/guides/smtp-vs-http-email-inboxes/). ## Minimal smtplib example This is the smallest useful SMTP example: ```python import smtplib message = "Subject: Welcome\r\n\r\nYour account is ready." with smtplib.SMTP("smtp.example.com", 587, timeout=30) as smtp: smtp.starttls() smtp.login("smtp-user", "smtp-password") smtp.sendmail("no-reply@example.com", ["user@example.com"], message) ``` That is fine for learning, but production code should use structured messages, environment-backed settings, and receive-side assertions. ## Configure SMTP settings with environment variables Use your deployment platform, shell, `.env` loader, or CI secret store to provide these values: ```bash SMTP_HOST=smtp.example.com SMTP_PORT=587 SMTP_USERNAME=smtp-user SMTP_PASSWORD=smtp-password SMTP_FROM_ADDRESS=no-reply@example.com SMTP_FROM_NAME="Example App" ``` Use port `587` with STARTTLS for most modern SMTP submission flows unless your provider documents another mode. Review [SMTP ports](/guides/what-are-smtp-ports/) and [STARTTLS vs SSL/TLS](/blog/starttls-ssl-tls/) when validating the setup. ## Send email with Python EmailMessage and smtplib `EmailMessage` keeps headers and body content clearer than hand-built strings: ```python import os import smtplib from email.message import EmailMessage message = EmailMessage() message["From"] = os.environ["SMTP_FROM_ADDRESS"] message["To"] = "recipient@example.com" message["Subject"] = "Welcome" message.set_content("Your account is ready.") with smtplib.SMTP(os.environ["SMTP_HOST"], int(os.environ["SMTP_PORT"]), timeout=30) as smtp: smtp.starttls() smtp.login(os.environ["SMTP_USERNAME"], os.environ["SMTP_PASSWORD"]) smtp.send_message(message) ``` Keep exception handling around the send call in application code so SMTP failures are logged and surfaced to your job runner. ## Send HTML email from Python Add a plain text body first, then attach the HTML alternative: ```python import os import smtplib from email.message import EmailMessage message = EmailMessage() message["From"] = os.environ["SMTP_FROM_ADDRESS"] message["To"] = "recipient@example.com" message["Subject"] = "Reset your password" message.set_content("Use the secure link in this email to reset your password.") message.add_alternative( """

Password reset

Use the secure link in this email to reset your password.

""", subtype="html", ) with smtplib.SMTP(os.environ["SMTP_HOST"], int(os.environ["SMTP_PORT"]), timeout=30) as smtp: smtp.starttls() smtp.login(os.environ["SMTP_USERNAME"], os.environ["SMTP_PASSWORD"]) smtp.send_message(message) ``` For release-critical HTML, run [email client testing](/testing/email-client-testing/) and [deliverability testing](/testing/email-deliverability-test/) before sending broadly. ## Send attachments from Python Use `pathlib` and `mimetypes` so attachment handling is explicit: ```python import mimetypes from pathlib import Path attachment_path = Path("reports/invoice.pdf") if not attachment_path.is_file(): raise FileNotFoundError(attachment_path) content_type, _ = mimetypes.guess_type(attachment_path) maintype, subtype = (content_type or "application/octet-stream").split("/", 1) message.add_attachment( attachment_path.read_bytes(), maintype=maintype, subtype=subtype, filename=attachment_path.name, ) ``` After changing attachment code, send to a MailSlurp inbox and assert the expected filename, content type, and attachment count. ## Send email from Python with the MailSlurp API For API-first tests or scheduled jobs, send from a MailSlurp inbox: ```python import json import os import urllib.request api_key = os.environ["MAILSLURP_API_KEY"] inbox_id = os.environ["MAILSLURP_INBOX_ID"] payload = json.dumps( { "to": ["recipient@example.com"], "subject": "Python API smoke test", "body": "Sent from a Python job through MailSlurp.", } ).encode("utf-8") request = urllib.request.Request( f"https://api.mailslurp.com/inboxes/{inbox_id}/confirm", data=payload, method="POST", headers={ "x-api-key": api_key, "Content-Type": "application/json", }, ) with urllib.request.urlopen(request, timeout=30) as response: sent_email = json.loads(response.read().decode("utf-8")) ``` This path is useful when you want API response data and test assertions without depending on a local SMTP session. ## Wait for the received email For tests, wait for a MailSlurp inbox to receive the message and assert the content: ```python import json import os import urllib.parse import urllib.request api_key = os.environ["MAILSLURP_API_KEY"] receive_inbox_id = os.environ["MAILSLURP_RECEIVE_INBOX_ID"] query = urllib.parse.urlencode( { "inboxId": receive_inbox_id, "timeout": 120000, "unreadOnly": "true", } ) request = urllib.request.Request( f"https://api.mailslurp.com/waitForLatestEmail?{query}", headers={"x-api-key": api_key}, ) with urllib.request.urlopen(request, timeout=130) as response: email = json.loads(response.read().decode("utf-8")) assert email["subject"] == "Python API smoke test" assert "Python job" in email.get("body", "") ``` That check proves more than SMTP acceptance. It proves the workflow produced a readable email in the expected inbox. ## Common Python SMTP errors and fixes ### 535 authentication failed Check credentials, app-password requirements, tenant policy, and sender-domain alignment. Then verify the from address is allowed by the SMTP provider. Use the [SMTP authentication guide](/blog/smtp-authentication/) for the full checklist. ### TLS or certificate failures Confirm the port and TLS mode. Port `587` commonly expects `starttls()`, while port `465` uses SMTP over SSL. If you need SSL mode, use `smtplib.SMTP_SSL` and validate provider settings. ### Connection timed out Check firewall rules, hosting-provider outbound SMTP restrictions, DNS, and proxy configuration. Add an explicit timeout so jobs fail clearly instead of hanging. ### Message accepted but never arrives Inspect headers, SPF, DKIM, DMARC, spam score, blacklist status, and inbox placement: - [Email header analyzer](/tools/email-header-analyzer/) - [SPF checker](/tools/spf-checker/) - [DKIM checker](/tools/dkim-checker/) - [DMARC checker](/tools/dmarc-checker/) - [Email blacklist checker](/tools/email-blacklist-checker/) - [Email spam checker](/tools/email-spam-checker/) ## Production checklist for Python email Before shipping Python email changes: 1. Keep SMTP and API secrets outside source code. 2. Use `EmailMessage` for headers, HTML, and attachments. 3. Validate port, TLS, authentication, and sender-domain policy. 4. Add timeouts and useful error logging around SMTP/API calls. 5. Send to a MailSlurp inbox and assert subject, body, links, codes, and attachments. 6. Re-test after template, DNS, or provider changes. 7. Use webhooks to track delivery, bounces, and downstream workflows. Start with [Email Sandbox](/product/email-sandbox/) for isolated send-and-receive tests, [email integration testing](/product/email-integration-testing/) for CI assertions, and [email webhooks](/guides/email-webhooks/) for delivery evidence. ## FAQ ### Is smtplib enough to send email in production? Yes for many workflows, if you use explicit TLS/auth settings, structured messages, timeouts, and receive-side assertions. The fragile part is usually not `smtplib`; it is untested configuration and deliverability. ### Can Python send HTML email? Yes. Use `EmailMessage.set_content()` for the text body and `add_alternative(..., subtype="html")` for HTML. ### Can Python send attachments? Yes. Use `EmailMessage.add_attachment()` with bytes, MIME type, and filename. Verify received attachments in a test inbox before release. ### How do I test Python email in CI? Send to a MailSlurp inbox, call wait-for-email, and assert subject, body, links, OTP codes, headers, and attachments before the job passes. ## Next steps - [SMTP and IMAP guide](/guides/smtp-imap/) - [Email Sandbox setup](/product/email-sandbox/) - [Email integration testing](/product/email-integration-testing/) - [Deliverability testing workflow](/testing/email-deliverability-test/)