Latest Articles
How to Fix Redirect Loops and ERR_TOO_MANY_REDIRECTS
A step-by-step way to find the URLs that redirect to each other, and the most common causes and fixes.
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Cron Syntax Explained: A Complete Guide to Cron Expressions
What each cron field means, how ranges and steps are matched, and how to read an expression without guessing.
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Five-Field vs. Six-Field Cron Expressions
The number of fields does not identify a cron dialect. Here is what changes between schedulers and why you cannot just add or drop a field.
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Why Day-of-Month and Day-of-Week Behave Differently in Cron
Why 0 0 13 * 5 is not 'Friday the 13th' in Unix cron, and how Spring, Quartz and EventBridge treat the same fields.
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Cron and Daylight-Saving Time: Skipped and Repeated Runs
A job at 02:30 may not run on the spring-forward day, and a job at 01:30 may match twice in autumn. Here is what to expect and how to plan around it.
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How to Read Email Headers
A practical, field-by-field guide to reading raw email headers and knowing which lines to trust.
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How to Trace an Email Using Its Headers
Follow the Received chain from the first server to your mailbox, and learn what an email trace really shows.
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SPF vs DKIM vs DMARC Explained
Three standards, three different identities. Here is what each one checks and how DMARC combines them.
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What Is an Authentication-Results Header?
How receiving servers record SPF, DKIM and DMARC outcomes, and how to read the fields.
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How to Read Received Headers
Break a Received header into its clauses and follow a message hop by hop.
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How Email Delivery Works
From the send button to the inbox: the servers, protocols and DNS records that deliver a message.
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What Is a Return-Path?
The Return-Path is the bounce address: here is how it differs from From and what it does and does not prove.
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