Why email bounces, and what actually fixes it on Bounce & Redirect

Return-Path, DSNs and VERP: Where Bounces Actually Go

Wed, 28 Oct 2026 09:00:00 +0000

Every message carries two sender addresses. The one people see is the From: header inside the message. The one mail servers act on is the envelope sender, given in the MAIL FROM command of the SMTP conversation. When delivery fails, the failure report goes to the envelope sender. That single fact explains most of the confusion about “where did the bounces go?”

About Bounce & Redirect

Wed, 28 Oct 2026 00:00:00 +0000

Bounce & Redirect explains why email bounces and what actually fixes it. It is written for people who send newsletters or transactional mail (receipts, password resets, account notices) and are watching delivery get worse without a clear reason.

Feedback Loops and Spam Complaints: Thresholds and Protocol Requirements

Tue, 04 Aug 2026 16:10:00 +0000

When a recipient clicks the “Report Spam” or “Mark as Spam” button in their webmail interface, it triggers an immediate negative reputation event for the sending domain. To manage deliverability effectively, sending infrastructure must capture these user feedback signals, process them automatically, and keep overall complaint rates within strict provider boundaries.

List Hygiene and Sunset Policies: Protecting Domain Reputation

Wed, 15 Jul 2026 14:20:00 +0000

The size of an email list is a misleading engineering metric. In email deliverability, sending to 50,000 highly engaged recipients yields significantly higher inbox placement than broadcasting to 500,000 stale addresses with low open rates and high bounce ratios.

Sender Reputation Dynamics: How Mailbox Providers Rate Your Domain

Mon, 22 Jun 2026 09:45:00 +0000

When a mail server receives a message that passes SPF, DKIM, and DMARC checks, it faces a fundamental decision: deliver the message to the primary inbox, place it in the spam folder, or drop it entirely. That decision is governed by sender reputation.

SPF, DKIM, and DMARC: The Mechanics of Email Authentication

Tue, 02 Jun 2026 11:15:00 +0000

Email was originally designed without built-in verification mechanisms. Under the basic SMTP specification, any sending host can populate the From: header with any domain name, creating a massive vulnerability for domain spoofing and phishing attacks.

SMTP Reply Codes: Deciphering 4xx and 5xx Bounce Signals

Thu, 14 May 2026 08:30:00 +0000

When a sending Mail Transfer Agent (MTA) opens a TCP connection to a receiving Mail Exchange (MX) server on port 25, every step of the transaction is governed by the Simple Mail Transfer Protocol (SMTP). If the receiving server refuses to accept a message for final delivery, it transmits a numeric reply code accompanied by a human-readable diagnostic string.

Step-by-Step Guide to Diagnosing a Deliverability Drop

Fri, 01 May 2026 09:00:00 +0000

A sudden drop in email open rates or transactional delivery is rarely a mystery when approached with systematically organized diagnostics. When messages start landing in the spam folder or bouncing at the SMTP gateway, infrastructure teams must resist the urge to make random DNS changes or alter message copy blindly.

Contact

Mon, 01 Jan 0001 00:00:00 +0000

Bounce & Redirect is an independent reference on why email bounces and how to fix it. If you spot an error, a wrong RFC reference, or a bounce code the decoder reads badly, please write:

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Mon, 01 Jan 0001 00:00:00 +0000

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