Sender Reputation is the composite algorithmic trust score assigned to a sending IP address and domain by mailbox providers. In 2026, machine-learning filters evaluate negative signals (complaints, spam traps, invalid recipients) against positive behavioral engagement (opens, rep…
IP Warming is the disciplined, phased engineering process of increasing email transmission volume across newly provisioned dedicated IP addresses. Mailbox providers distrust brand-new IPs with zero historical sending footprint; attempting high-volume dispatch immediately results …
Directory-Based Edge Blocking (DBEB) is a perimeter security feature in Microsoft Exchange Online Protection (EOP) that rejects messages addressed to invalid recipients directly at the SMTP edge socket. Senders targeting Microsoft 365 enterprise tenants who generate high volumes …
The Junk Mail Reporting Program (JMRP) is Microsoft’s dedicated Feedback Loop (FBL) service. Whenever an Outlook.com, Hotmail, or Live.com subscriber clicks “Report Junk” or “Phishing”, Microsoft wraps the offending message in RFC 5965 Abuse Reporting Format (ARF) and forwards it…
Smart Network Data Services (SNDS) is Microsoft’s official IP reputation portal, providing senders with direct operational visibility into traffic volume, complaint rates, spam trap hits, and filter dispositions across Outlook.com, Hotmail, and Live.com. This guide explains how t…
DNS-Based Authentication of Named Entities (DANE), standardized under RFC 7672, binds TLS certificates directly to mail exchanger hostnames using DNSSEC-signed TLSA records. By eliminating reliance on centralized Certificate Authorities (CAs) and providing tamper-proof cryptograp…
SMTP TLS Reporting (TLS-RPT), standardized under RFC 8460, provides receiving domains with aggregated daily JSON telemetry from sending MTAs regarding TLS connection success rates and policy failures under MTA-STS and DANE. TLS-RPT gives email operators visibility into expired ce…
SMTP MTA Strict Transport Security (MTA-STS), defined in RFC 8461, upgrades opportunistic STARTTLS to mandatory encryption by establishing a cryptographic policy served over HTTPS. Backed by Google, Microsoft, and Yahoo, MTA-STS eliminates man-in-the-middle STRIPTLS downgrade att…
Authenticated Received Chain (ARC), standardized under RFC 8617, preserves email authentication results across forwarding intermediaries, mailing lists, and security gateways that modify message content and break SPF and DKIM signatures. ARC introduces a cryptographically sealed …
STARTTLS (RFC 3207) upgrades plain text SMTP connections to encrypted TLS sockets in-band, safeguarding email transmissions against passive wiretapping. Because classic STARTTLS is opportunistic by default, it remains vulnerable to active man-in-the-middle downgrade attacks (STRI…