Tag
smtp
- Sep 28, 2026 The Split Between Submission and Relay Ports Why port 587 exists separately from port 25, which policies differ between the two roles, and how a server distinguishes a user from a peer MTA. internet protocols
- Jun 26, 2026 Store-and-Forward Delivery and the MX Indirection How mail separated the address a sender writes from the host that receives it, why transfer is hop-by-hop rather than end-to-end, and what the retry rules actually require. computing history
- Jun 15, 2026 SPF Evaluation and Its Ten-Lookup Budget How a receiver matches a sending IP against a domain policy written in TXT records, why the recursion limit exists, and what each result value actually permits. internet protocols
- Nov 25, 2025 Queue Management and Retry Scheduling in MTAs How a mail server decides when to retry a failed delivery, why the four-hour and five-day thresholds exist, and how a permanent failure becomes a bounce. internet protocols
- Jun 23, 2025 ESMTP Extension Negotiation and Its Failure Modes How EHLO replaced HELO, what the keyword list in the reply actually guarantees, and why PIPELINING and CHUNKING change the shape of a session. internet protocols
- Jan 18, 2025 MX Resolution, Preference Ordering, and Null MX How a sending server turns a domain into a list of hosts, why the preference values are ordered the way they are, and what an empty MX list asserts. internet protocols
- Sep 13, 2023 Header Folding and the Line Limits That Shape MIME Encoding How the 998-octet line limit, dot-stuffing, and the 75-character encoded-word bound force the transfer encodings that mail still uses. internet protocols
- Nov 8, 2022 Envelope and Header Addresses in SMTP Delivery Why a message carries two independent sets of addresses, which one routing and bounces actually consult, and what breaks when a gateway rewrites one but not the other. internet protocols