Microsoft's Rejection Phase Is Live: A 550 5.7.515 Field Guide
Outlook now hard-rejects non-compliant bulk mail with 550 5.7.515, and Safe Senders cannot override it. Diagnosing the bounce and fixing the authentication behind it.
Articles and tutorials on communication infrastructure.
13–24 of 61 articles
Outlook now hard-rejects non-compliant bulk mail with 550 5.7.515, and Safe Senders cannot override it. Diagnosing the bounce and fixing the authentication behind it.
Gmail's January update puts Gemini between senders and readers: thread summaries, an AI-prioritized inbox, and suggested replies. What changes for email programs.
January is the quiet window between peak seasons. The full-stack audit that catches drift in authentication, DNS, list hygiene, and monitoring before it costs mail.
Microsoft joined the mandate, Gmail moved to hard rejection, and DMARCbis reached the finish line. What 2025 changed for senders and what it sets up for 2026.
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.
Postmaster Tools, SNDS, FBLs, DMARC reports, TLS-RPT, bounce logs, engagement data: the full observability stack, what each layer catches, and the alerts worth paging on.
Everyone has received the same email twice. The retry loops, queue semantics, and race conditions that cause duplicates, and the idempotency patterns that stop them.
Addresses like 佐藤@例え.jp are valid email. How EAI and SMTPUTF8 work, who supports them, and what sending systems break when a Unicode address shows up.
Email is a DNS application. The full record inventory a sending domain needs, the TTL strategy for safe changes, and the misconfigurations that quietly break delivery.
Between Black Friday and year end, send volumes triple while filters tighten. How to ramp into peak season so November's volume looks like growth, not an incident.
DMARCbis is finishing its journey through the IETF, replacing RFC 7489 with a Standards Track spec. The tree walk, retired tags, and what senders should do now.
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.