// how to fix
How to fix email problems
Your test or scan found a problem? Find the matching guide below: what it means, why it matters, and how to fix it step by step.
DNS 33
DMARC 28
SPF 28
DKIM 26
Reputation 24
Bounce 16
Security 16
Blacklist 13
Gmail 13
Content 12
Mailing list 11
Spam score 10
Headers 9
Reverse DNS 7
Mail server 4
Microsoft 365 4
MX 4
Outlook 4
TLS 2
Apple 1
BIMI 1
E-commerce 1
Google Workspace 1
WordPress 1
Yahoo 1
Zoho 1
16 guides · tag Bounce
| Problem | In short | Tags | |
|---|---|---|---|
| Gmail bounce "550 5.7.26": unauthenticated email | Gmail refused your email because it could not confirm it comes from your domain. SPF, DKIM or DMARC is missing or failing. Here is how to fix it. | Fix it | |
| Bounce "550 5.7.1": message rejected or blocked by policy | A 5.7.1 bounce means the receiving server refused your email on purpose. Learn to read bounce messages, find the real reason and fix it. | Fix it | |
| High bounce rate: clean your mailing list | Sending to addresses that no longer exist damages your reputation fast. Learn the difference between hard and soft bounces and remove bad addresses after every send. | Fix it | |
| Emails delayed: greylisting and 4xx temporary errors | Some servers answer "try again later" on purpose. A normal mail server retries and the email arrives a few minutes late. Here is how to tell normal delays from real problems. | Fix it | |
| Yahoo and AOL "421 4.7.0 [TSS04]" deferrals | Yahoo is temporarily refusing your emails because of their volume or complaints. Slow down, keep retrying, and fix what Yahoo does not like. | Fix it | |
| Emails blocked by Orange, SFR, Free or other French ISPs | French internet providers filter strictly with their own rules. Fix your reverse DNS and authentication, slow down, and use their contact procedures. | Fix it | |
| Your emails are not received at all: a step-by-step checklist | Your recipients say nothing arrived, not even in spam. Follow these steps in order to find where the email gets lost. | Fix it | |
| Use double opt-in for your newsletter | Ask every new subscriber to confirm their address with one click. Your list stays clean, bounces and complaints drop, and your emails reach the inbox more often. | Fix it | |
| Emails to Apple "Hide My Email" addresses (privaterelay.appleid.com) | Users who sign up with Apple can hide their real address behind a relay. Your emails reach them only if you register your sending domain with Apple and authenticate it. | Fix it | |
| Bounce "550 5.1.1": the address does not exist | The receiving server says the mailbox does not exist. Check the spelling, remove the address from your lists, and keep your bounce rate low. | Fix it | |
| Bounce "552 5.2.2": the mailbox is full | The recipient has run out of storage space. It is their problem, not yours, but repeated "mailbox full" bounces often mean an abandoned address. | Fix it | |
| "554 5.7.1 Relay access denied" when sending | Your mail server refuses to pass your email on because you are not logged in. Usually a missing SMTP login or the wrong port in your app or printer. | Fix it | |
| Microsoft 365 "550 5.1.8 Access denied, bad outbound sender" | Microsoft 365 has blocked a user from sending because the account sent spam, usually after being hacked. Secure the account, then unblock it. | Fix it | |
| Gmail "421 4.7.28": unusual rate of unsolicited mail | Gmail is slowing down your emails because it sees a sudden spike or spam-like traffic from your IP or domain. Slow down and fix your reputation. | Fix it | |
| Microsoft "451 4.7.500 Server busy": temporary deferral | Outlook.com and Hotmail are holding back emails from your IP because they do not know it or trust it yet. Keep volumes low and build reputation. | Fix it | |
| Gmail bounce "550 5.7.25": reverse DNS (PTR) required | Gmail refuses your email because your sending IP has no reverse DNS, or one that does not point back to the IP. Ask your host to set a proper PTR. | Fix it |
Not sure what is wrong?
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