{
  "id": 8486788,
  "title": "I Sent 50 Emails And Got 12 Bounces. SMTP 250 Failed Me.",
  "url": "https://urgent.news/2026/09/19/i-sent-50-emails-and-got-12-bounces-smtp-250-failed-me",
  "topic": "tech",
  "section": "Tech",
  "published": "2026-09-19T15:41:33.000Z",
  "source": {
    "name": "Dev.to",
    "slug": "dev-to",
    "url": "https://dev.to/onizuka/i-sent-50-emails-and-got-12-bounces-smtp-250-failed-me-5gi4"
  },
  "original_language": "en",
  "account": "On July 15, the author queued a campaign to send 50 emails to verified addresses using a plain SMTP handshake. To their surprise, every single one of those emails returned a 250 OK response, indicating successful delivery, despite the addresses appearing healthy in the logs. Three hours later, the author found that twelve of those emails had bounced, resulting in a 24% failure rate in just 38 minutes.\n\nCurious about the cause of this unexpected failure, the author decided to run the same list through a more comprehensive email validator. The validator examines various factors such as MX behavior, breach history, role-account flags, and provider identity. The validation process for test@gmail.com provided some unsettling results. The request to validate the email was made using a GET request, with headers including the RapidAPI key and host.\n\nThe response from the validator indicated that the email was valid in terms of syntax and had an MX record found. However, it was marked as an is_role address, specifically a test email account. The email was classified as a disposable email, which likely contributed to its bounce. Additionally, the email had a breach history, with 579 recorded breaches, including exposures of email addresses, passwords, and various other data classes.\n\nThe author concluded that the SMTP handshake had failed to reveal these issues, as the SMTP_varified field in the validator's response was null. This incident highlights the importance of using robust email validation methods beyond simple SMTP checks to ensure reliable email delivery and avoid potential issues.",
  "summary": "api, #cybersecurity, #webdev, #python On July 15 I queued a campaign to fifty addresses I had already \"verified\" with a plain SMTP handshake. Every single one returned 250 OK . Three hours later, twelve of them bounced. That's a 24% failure rate in 38 minutes on addresses that looked perfectly healthy in the logs. The code that reproduces the failure is on GitHub . This time I wanted to know what…",
  "key_points": [
    "Author queued 50 emails for delivery using plain SMTP handshake",
    "All 50 emails returned 250 OK response, indicating successful delivery",
    "12 emails bounced within 38 minutes, resulting in 24% failure rate"
  ],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}