Email verification glossary
Every term you will meet in a bounce report, a verification result or a deliverability guide, explained in plain English. Each entry says what the term means, why it matters for your list, and how a verifier handles it.
Bounces
- Hard bounceA hard bounce is an email that the receiving server rejected permanently. The address does not exist, the domain does not exist, or the server blocked your email. Sending the same email again will fail again.
- Mailer-daemonThe mailer-daemon is the part of a mail server that sends automatic messages. Most of these messages are bounce notices. A message from mailer-daemon means an email you sent was not delivered.
- Soft bounceA soft bounce is an email that was not delivered this time because of a temporary problem. The address is real. The inbox is full, the server is busy, or the server asked you to try again later.
Authentication and DNS
- MX recordAn MX record is a DNS record that says which server receives email for a domain. When you send to name@example.com, your mail server looks up the MX record for example.com to find the server to deliver to.
- PTR recordA PTR record is a DNS record that connects an IP address to a hostname. It is the reverse of a normal DNS record. Mail servers check the PTR record of the IP address that is sending to them. Some servers reject email from IP addresses that have no PTR record.
- SPF recordAn SPF record is a DNS record on your domain that lists the servers allowed to send email for that domain. Receiving servers check it to confirm that an email claiming to come from your domain was sent by one of your servers.
Deliverability
- GreylistingGreylisting is a spam defence. A mail server rejects the first email from a sender it does not know. It accepts the same email when the sender tries again a few minutes later. Real mail servers retry. Most spam software does not.
- Spam filterA spam filter is the system a mailbox provider uses to decide if an incoming email goes to the inbox, to the spam folder, or is rejected. It checks the sender, the email content, and how past recipients reacted to emails from that sender.