Every AI, email, and agent term explained for developers. From context engineering to DKIM.
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A holding area for messages that couldn't be processed or delivered after exhausting all retry attempts.
A DNS-based email authentication method that lets receiving servers verify a message was actually sent and unmodified by the domain it claims to come from.
An email policy protocol that tells receiving servers what to do when SPF or DKIM checks fail for messages claiming to be from your domain.
The requirement that the domain in SPF or DKIM authentication matches the domain in the email's visible From header.
The return-path address used during SMTP transmission, which may differ from the visible From address the recipient sees.
A retry strategy where the wait time between attempts increases exponentially, reducing load on failing systems.
An anti-spam technique where a mail server temporarily rejects emails from unknown senders, expecting legitimate servers to retry.
A permanent email delivery failure caused by an invalid address, non-existent domain, or blocked recipient.
A cryptographic hash used to verify that a webhook payload was sent by a trusted source and hasn't been tampered with.
A property where performing the same operation multiple times produces the same result as performing it once.
The practice of gradually increasing email volume from a new IP address to build sender reputation with email providers.
A DNS record that specifies which mail server should receive email for a domain.
A score that email providers assign to a sending domain or IP address based on its email-sending behavior and history.
A server that forwards outbound email on behalf of another system, handling delivery, authentication, and retry logic.
Three-digit status codes returned by mail servers during SMTP transactions to indicate success, temporary failure, or permanent rejection.
A temporary email delivery failure where the message may succeed if retried, typically caused by a full mailbox or server issue.
A DNS record that lists which mail servers are authorized to send email on behalf of your domain.
A list of email addresses that should never receive messages, typically populated by hard bounces, unsubscribes, and spam complaints.
An HTTP callback that sends real-time event data to your application when something happens, like an email being delivered or bouncing.