Category: Email Deliverability

Practical guides to domain authentication, sender reputation, routing, and reliable email delivery.

Return Path Domain Setup: 5 DNS Steps for DMARC

Configure a return path domain, verify SPF and DMARC alignment, inspect message headers, and monitor bounce handling with current Sendmux DNS records.

Sendmux Team24 days ago10m

Envelope sender passing through SPF and DMARC alignment checks before delivery

How to Send Email via API: A Developer Guide

Send email via API with a valid request, scoped key, uploaded attachments, idempotent retries, delivery events, and current Sendmux examples.

Sendmux Team27 days ago8m

JSON email request moving through an authenticated API to a queued message ID

SMTP Port 587 vs 2525: Which Should You Use?

Choose between SMTP ports 587 and 2525, match the correct TLS mode, and diagnose blocked connections without weakening authentication or certificate checks.

Sendmux Team28 days ago8m

SMTP client choosing port 587 before a documented port 2525 fallback

Email Rate Limiting for Safe, Predictable Sending

Queue email before sending, enforce the right counters, and handle HTTP or SMTP pressure without delaying urgent messages or creating duplicates.

Sendmux Team29 days ago8m

Email traffic classes entering a quota-controlled sending queue

DMARC for SaaS Teams: A Safe Enforcement Playbook

Map every SaaS sending identity, process DMARC aggregate reports, and move from monitoring to enforcement without breaking critical email.

Sendmux TeamAug 22, 20268m

DMARC monitoring, remediation, and enforcement gates for SaaS email

Bounce Handling Guide for Reliable Email Workflows

Build a bounce handling pipeline that classifies DSNs, avoids duplicate retries, enforces recipient suppression, and processes signed email events.

Sendmux TeamAug 22, 20267m

Bounce events passing through classification, suppression, and monitoring gates

Cold Email Batching: A Safer Scaling Workflow

Learn how to batch cold email with consent, authentication, quota-aware queues, retry controls, suppression, and measurable stop signals.

Sendmux TeamAug 21, 202610m

Cold email cohorts passing through eligibility, authentication, queue, and feedback gates

DMARC Alignment: Relaxed vs Strict Modes

Learn how DMARC alignment connects the visible From domain to SPF or DKIM, when relaxed and strict modes pass, and how to diagnose failures.

Sendmux TeamAug 21, 20266m

Relaxed and strict DMARC alignment paths comparing From, SPF, and DKIM domains

Reply Threading: How Email Conversations Stay Linked

Learn how Message-ID, In-Reply-To, References, provider thread IDs, and raw-header checks keep email replies in the right conversation.

Sendmux TeamAug 20, 20266m

Three email messages connected by Message-ID, In-Reply-To, and References headers

Best Email Attachments API for Developers

Choose an email attachments API pattern for base64, binary uploads, reference IDs, inbound downloads, agent workflows, security, and provider limits.

Sendmux TeamAug 20, 20269m