Kalenfy blog · section
Fixes & troubleshooting
All our fixes & troubleshooting guides
Fixes & troubleshooting
27 June 2026
Common SMTP Error Codes (4xx & 5xx) Explained
Got an SMTP error like 550 or 421 on a bounced email? Here's what the common 4xx and 5xx SMTP codes mean in plain English, and what to do about each one. With a free domain check.
Fixes & troubleshooting
27 June 2026
Why Does My Email Go to Gmail's Promotions Tab?
Your email landing in Gmail's Promotions tab isn't spam — but it's less visible. Here's why Gmail sorts mail there, whether it matters, and how to land in the Primary inbox more often.
Fixes & troubleshooting
27 June 2026
What Is a Spam Trap? (And How to Avoid One)
Spam traps are hidden email addresses that catch senders with poor list hygiene — and hitting one can get you blacklisted. Here's what spam traps are and how to stay clear of them.
Fixes & troubleshooting
27 June 2026
What Is Greylisting? (Why First Emails Are Delayed)
Greylisting temporarily defers email from unknown senders, so the first message can arrive minutes late. Here's what greylisting is, why it works against spam, and what to do about it.
Fixes & troubleshooting
27 June 2026
Soft Bounce vs Hard Bounce (Email Bounces Explained)
A hard bounce is a permanent delivery failure; a soft bounce is temporary. Here's the difference, what causes each, and how to handle bounces so they don't wreck your sender reputation.
Fixes & troubleshooting
27 June 2026
How to Get Off an Email Blacklist
Your email is being blocked because your domain or IP is on a blacklist. Here's how to check which one, fix the cause, request delisting, and stop it happening again. Free check.
Fixes & troubleshooting
27 June 2026
What Is DNS Propagation? (Why Changes Take Time)
Just changed a DNS record and nothing's happening? That's DNS propagation. Here's what it really is, how long it takes, why TTL matters, and how to check — with a free scan.
Fixes & troubleshooting
27 June 2026
How to Redirect HTTP to HTTPS (Force HTTPS)
Stop the 'Not secure' warning by forcing every visitor onto HTTPS. Here's how to redirect HTTP to HTTPS on Apache, Nginx and Cloudflare — and lock it in with HSTS. Free check.
Fixes & troubleshooting
27 June 2026
SPF ~all vs -all: Soft Fail vs Hard Fail
What's the difference between ~all and -all in an SPF record? Here's soft fail vs hard fail in plain English, which to use, and why the wrong one leaves you spoofable. Free check.
Fixes & troubleshooting
27 June 2026
DMARC p=none vs reject: Moving Safely to Enforcement
DMARC at p=none only monitors — it doesn't stop spoofing. Here's the difference between p=none, quarantine and reject, and how to move to enforcement without blocking real mail.