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Field notes on diagnosing deliverability. What actually causes placement problems, and why the obvious fix is usually the wrong one.
Start here · The complete guide

Email deliverability: the complete diagnostic guide

What actually decides whether mail reaches the inbox, and the six checks I run, in order, to find which cause is yours. The method behind everything else on this blog.
23 min read
GUIDE
Symptom · Spam
11 min read

Why your emails are going to spam, and why most fixes don't work

Every guide gives you a checklist. None of them explain how to tell which item on it is actually your problem.
Gmail · Spam
8 min read

The 6 most common causes of Gmail spam placement, and how to diagnose each

Most spam placement traces back to one of six causes. They all look identical from the outside.
Domain Warmup
6 min read

Domain warmup: what most guides get completely wrong

A generic warmup schedule can be worse than no warmup at all. Here's why, and what to do instead.
SPF · DMARC
7 min read

Why your SPF record might be actively making things worse

Multiple SPF records, ~all vs -all, and the lookup limit that quietly kills senders who think they're fine.
Reputation
7 min read

Shared IP pools: when your reputation isn't yours

How a neighbor on the same IP block can tank your placement, and how to tell if it's happening to you.
Spam Placement
8 min read

How to stop emails going to spam, in the order I actually check

Most advice hands you twelve things to fix and never says which one is yours. This is the sequence I actually run instead.
Gmail · Postmaster
7 min read

How the Gmail spam filter actually decides where your mail goes

Google publishes a hard threshold you can measure yourself. What it doesn't publish is how the pieces interact.
DMARC · Policy
8 min read

DMARC p=reject, what it actually does and when to set it

Most of the damage from p=reject hits senders who set it correctly and had no idea what it would do to forwarded mail.
IP Warmup
6 min read

IP warmup schedule: what should actually set your ramp

Warmup works. A generic day-count schedule that ignores your list, volume and mailbox providers doesn't.
Bounce Codes
6 min read

Soft bounce vs hard bounce, and the difference that actually matters

Temporary versus permanent is the textbook answer. It hides the part worth knowing: a hard bounce doesn't reliably mean the address is bad.
Bounce · 550
3 min read

550 5.7.1: what this bounce actually means

The receiving server accepted your message and refused it for a policy reason. How I tell an authentication gap from a reputation problem.
Bounce · 550
3 min read

550 5.1.1: what this bounce actually means

The receiving server found no mailbox at that address. How I tell a genuinely dead address from a typo or a full mailbox.
Bounce · SMTP 421
3 min read

SMTP 421: what this response actually means

A 421 is the server closing the connection, not rejecting your message. How to tell a capacity blip from a reputation throttle.
Blocklist · UCEPROTECT
3 min read

UCEPROTECT: what Levels 1, 2 and 3 actually mean

UCEPROTECT runs three separate lists. Which one is blocking you decides who can actually fix it.
Blocklist · Spamhaus
3 min read

Spamhaus DBL: what actually gets a domain listed

The DBL lists domains by how they were used in mail traffic, not by who owns them.
Setup · GoDaddy
3 min read

DKIM for GoDaddy: where the record actually goes

GoDaddy hosts your DNS, not your email. Exactly where the DKIM record goes, and why most failures aren't GoDaddy's fault.
Setup · Workspace
3 min read

DKIM for Google Workspace: the actual setup steps

Generated in the Admin console, not your DNS panel. The exact steps, and why it's the first thing worth checking.
Setup · Workspace MX
3 min read

Google Workspace MX record: the exact values

One value, repeated. The exact record, and what a correct MX record doesn't fix on its own.
Glossary · DMARC
1 min read

What is DMARC?

Resolves the one thing SPF and DKIM can't decide alone: what happens after an authentication check fails.
Glossary · DKIM
1 min read

What is DKIM?

Confirms a message wasn't altered and that a domain authorized it. It doesn't check the address you actually see.
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Julian Turgelski
The Diagnostic Blog About Privacy Terms
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