Greylisting, Tarpitting, and Other Receiver Defenses Senders Should Understand
Receiving servers defend themselves with deliberate delays, temporary rejections, and traps for impatient senders. How each defense works and how a good MTA passes them.
7 articles with this tag
Receiving servers defend themselves with deliberate delays, temporary rejections, and traps for impatient senders. How each defense works and how a good MTA passes them.
Every sending platform offers SMTP relay and an HTTP API. The differences in latency, error handling, portability, and observability, and how to choose per workload.
Validation APIs verify syntax, domains, and mailbox existence. Where each check works, where catch-alls and traps defeat them, and where validation belongs in your stack.
Every delivery question has its answer in the headers. How to trace a message's path through Received lines and decode Authentication-Results like a postmaster.
TLS-RPT delivers daily JSON reports on every failed TLS negotiation to your domain. The record, the report format, and how to turn failures into fixes.
MTA-STS closes the STARTTLS downgrade hole by letting domains require verified TLS for inbound mail. The policy file, the DNS record, and the gotchas in between.
Hard versus soft is not enough. How SMTP codes, enhanced status codes, and provider quirks should drive your retry, suppression, and reputation logic.