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What can cause an email to bounce?
Updated over a month ago

The emails we provide come from trusted sources, and we have a strong level of confidence in their accuracy. While no dataset is perfect, it's unlikely that incorrect email addresses are a widespread issue.

If an email bounces, it's more often due to how it was sent rather than the validity of the address itself. Common reasons for bounces include:

  • Unknown email or invalid address – The recipient’s email doesn’t exist or was mistyped.

  • Spam filter triggers – The email content, links, or sender details may have set off spam defenses.

  • Blacklisted sender – The IP address, sending email, or domain is flagged on a blocklist.

  • Email subject or content issues – Certain words, phrases, or formatting can cause rejection.

  • Attachment restrictions – Many providers block emails with attachments from unknown senders.

  • Policy filtering – The recipient’s email system has specific rules that rejected the message.

  • Server misconfiguration – Either the sender's or recipient's mail server is not set up correctly.

  • Full inbox – The recipient’s mailbox has reached its storage limit.

  • Greylisting – A temporary rejection, where the recipient’s server asks the sender to try again later.

  • Overloaded recipient server – The receiving mail server is experiencing heavy traffic.

  • Low sender reputation – If the sending domain or IP has a poor reputation, messages may be rejected.

If you’re seeing a high bounce rate, it may help to review email sending practices and ensure your domain, IP, and content align with best practices.

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