// how to fix
Not sure what is wrong?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.
Bounce 40
DNS 36
DMARC 33
Reputation 33
SPF 30
DKIM 27
Gmail 19
Security 19
Blacklist 18
Content 14
Headers 11
Mailing list 11
Spam score 11
Reverse DNS 10
Microsoft 365 8
Outlook 8
Mail server 7
MX 5
Yahoo 4
TLS 3
Apple 2
Google Workspace 2
BIMI 1
E-commerce 1
GMX 1
WordPress 1
Zoho 1
10 guides · tag Reverse DNS
| Problem | In short | Tags | |
|---|---|---|---|
| No reverse DNS (PTR), or it does not match | Reverse DNS gives a name to your server's IP address. Without it, or if it does not point back, your server looks like an infected home computer. | Fix it | |
| Invalid HELO/EHLO hostname | Your server introduces itself with a name that is not valid, such as localhost or a bare IP. Spam filters distrust this. Give it a real name that matches reverse DNS. | Fix it | |
| Running your own mail server: the deliverability checklist | A self-hosted Postfix server can deliver well, but only if every basic is right: reverse DNS, SPF, DKIM, DMARC, TLS and no open relay. | Fix it | |
| How to set reverse DNS (PTR) at your hosting company | The PTR record of your server IP is set by your hosting company, not in your domain DNS. Here are the general steps at OVH, Hetzner, Scaleway, AWS and DigitalOcean. | 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 IP is on the Barracuda blacklist (BRBL) | Barracuda devices block emails from IPs on its reputation list. Find out why you were listed, fix the cause, then ask for removal for free. | 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 | |
| Yahoo / AOL "553 5.7.1 [BL21] Connections will not be accepted ... Spamhaus's list" (BL23): how to fix it | Yahoo and AOL refuse your server because its IP is on a Spamhaus list. Find which list, fix the cause, get delisted and resend. | Fix it | |
| GMX / WEB.DE "554 Transaction failed / Reject due to policy restrictions" and "invalid DNS PTR resource record": fix | GMX and WEB.DE refuse servers without a valid reverse DNS (PTR) or with a poor reputation. How to read the error and fix your server. | Fix it | |
| "450 4.7.1 Client host rejected: cannot find your hostname" (or "reverse hostname"): how to fix it | The receiving server could not match your IP to a hostname. Fix the reverse DNS (PTR) and its matching A record to stop this bounce. | Fix it |
Not sure what is wrong?
Send a test email or scan your domain: the report tells you which problem you have.