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Practical field notes for teams diagnosing email deliverability, DNS authentication, sender reputation, Linux, MTA, cloud, monitoring, and DevOps failures.

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Technical knowledge system connecting email identity, secure mail flow, servers, cloud operations, monitoring, and runbooks

182 Published articles

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Technical notes

Articles on email deliverability, DNS, Linux, MTA operations, DevOps, monitoring, and incident recovery.

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Short, practical guidance for teams that need to diagnose, repair, and run production email systems.

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Two Linux server networking designs compare an active link with a standby failover path and a pair of active links grouped through an LACP switch

Linux, MTA & Security · Aug 22, 2021 · 18 min read

Linux Ethernet Bonding: Active-Backup and LACP with NetworkManager

Build and test Linux Ethernet bonding with NetworkManager or Netplan, including active-backup, 802.3ad LACP, monitoring, troubleshooting, and rollback.

Email Deliverability · Jul 23, 2021 · 12 min read

Gmail BIMI Support in 2021: DMARC-Enforced Brand Logos Arrive

An expert guide to Gmail’s July 2021 BIMI launch, from enforced DMARC and verified logo evidence to safe rollout and realistic measurement.

Labelled Apple Mail Privacy Protection flow showing sender image host, Apple privacy relay, background content download, masked IP and outcome-based measurement

Email Deliverability · Jun 28, 2021 · 12 min read

Apple Announced Mail Privacy Protection in 2021: Open Measurement Changed

A technical and operational guide to Apple’s 2021 Mail Privacy Protection announcement and the measurement redesign it required from email teams.

Client traffic enters one floating virtual IP owned by an active Linux IPVS director, while a synchronized standby director and health checks protect multiple real servers

Linux, MTA & Security · Jun 3, 2021 · 24 min read

Linux Virtual Server High Availability with IPVS and Keepalived

Build and operate a two-director Linux Virtual Server with IPVS, Keepalived VRRP, backend health checks, NAT or Direct Routing, state synchronization, failover testing, and rollback.

Layered application traffic becomes Ethernet frames, crosses a switch and router between subnets, and connects wired, wireless, VLAN, IPv4, IPv6 and NAT concepts

Linux, MTA & Security · May 14, 2021 · 85 min read

Networking Basics: Ethernet, IP, Routing, Switching, VLANs, IPv6 and NAT

Comprehensive networking notes covering Ethernet, CSMA/CD, MAC and ARP, IP flow, switching, routing, OSI, subnetting, RIP, EIGRP, OSPF, wireless, VLANs, Frame Relay, IPv6 and NAT.

Email delivery decision path separating successful delivery, temporary retry, and permanent suppression with investigation

Email Deliverability · May 14, 2021 · 19 min read

Soft and Hard Bounce Errors

Classify SMTP and DSN outcomes safely, decide retry and suppression separately, then use the complete unchanged Soft and Hard Bounce Rules reference.

Labelled Microsoft 365 external sender workflow showing external origin classification, Exchange Online tenant policy, Outlook indicator and controlled exceptions

Email Deliverability · Apr 25, 2021 · 12 min read

Microsoft 365 External Email Labels in 2021: New Recipient Trust Signals

A practical guide to Microsoft’s 2021 native External sender callout and what enterprise senders, marketers and support teams should do about it.

An email complaint enters separate forensic and aggregate feedback paths before validated suppression, investigation, trend analysis, and sending-program correction

Email Deliverability · Apr 7, 2021 · 19 min read

Email Complaint Feedback Loops: FBL Enrollment, Processing, and Suppression

Enroll in Yahoo, Microsoft, Gmail, and multi-provider feedback loops, then process ARF and aggregate complaints safely with suppression, monitoring, and incident controls.

Connected email standards ecosystem linking message format, transport, DNS, authentication, security, mailbox access, filtering, and reporting layers

Email Deliverability · Apr 7, 2021 · 15 min read

Email Standards Based on RFCs: A Practical Reference

A practical map of the RFCs behind SMTP, message format, MIME, IMAP, POP3, JMAP, authentication, transport security, reports, mailing lists, Sieve, and internationalized email.