Category Definitions
Below is a comprehensive list of the categories mailfloss uses to classify email addresses during verification.
Email addresses that fail syntax checks and are deemed invalid.
Email addresses flagged as potential spam accounts.
Addresses associated with roles (e.g., "administrator"). While these emails may be valid, they often underperform and can negatively impact deliverability rates.
Email addresses containing banned keywords or domains, such as offensive language or patterns associated with fake or poor-quality addresses.
Temporary email addresses provided by disposable email services. These are unreliable and negatively affect deliverability.
Addresses associated with domains lacking valid MX records, making them incapable of receiving emails. These are marked as "illegit" in reports.
Email addresses linked to inactive domains or domains listed as parked or for sale. Such addresses are typically invalid.
Addresses that appear valid but cannot be fully verified due to non-responsive domains.
Email addresses flagged for containing user-defined blacklisted keywords.
Addresses that have previously resulted in email bounces, making them risky to use.
Addresses that have reported emails as spam in the past, indicating a higher likelihood of future complaints.
Addresses determined to be non-existent through testing.
Addresses that have been deactivated and can no longer receive incoming emails.
Addresses unable to receive emails because the recipient's inbox is over quota.
Addresses that fail Microsoft Exchange testing and pose a high risk of hard bounces. Sending emails in bulk to these addresses is not advised.
Domains configured to accept all emails appear valid but cannot be fully verified. For example, a domain like mailfloss.com might validate both [email protected] and [email protected]. Since such domains do not confirm individual addresses, these are flagged as "accept_all" in reports.
Verification was skipped for this address, often because the user's plan limits have been reached.
We’re constantly improving our verification processes and algorithms. If you believe an email has been miscategorized, please reach out to us. For manual verifications, you can report errors by clicking the “Report as Incorrect” button.
