// 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
33 guides · tag Reputation
| Problem | In short | Tags | |
|---|---|---|---|
| Your emails land in Gmail's spam folder | When Gmail sends your emails to spam, the cause is almost always authentication, reputation or content. Here is how to find which one and fix it. | Fix it | |
| Your emails land in Outlook or Hotmail junk | Outlook.com, Hotmail and Live send many new senders to Junk. Check your setup, then use Microsoft's free sender tools: SNDS, JMRP and the delist portal. | 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 | |
| Warm up a new domain or IP address | A new domain or IP has no reputation yet. Sending a large campaign on day one looks like spam. Start small and increase your volume step by step. | 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 | |
| Spam traps and bought email lists | Spam traps are hidden addresses that catch senders with bad lists. Hitting them can blacklist you. Never buy lists, and only email people who asked for it. | 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 | |
| Use a subdomain for marketing emails | Sending newsletters from a subdomain such as news.yourdomain.com keeps their reputation apart from your everyday business emails. Here is how to set it up. | Fix it | |
| Cold emailing without landing in spam | Prospecting emails are judged harshly by Gmail and Outlook. Protect your main domain, send slowly, write like a person and make opting out easy. | Fix it | |
| Too many people mark your emails as spam | A high spam complaint rate sends all your emails to junk. Learn how to measure complaints, get feedback loops and send only to people who want your emails. | 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 | |
| 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 | |
| Keep transactional and marketing emails apart | Receipts and password resets should never suffer because a newsletter got complaints. Send each kind of email through its own provider, stream or subdomain. | Fix it | |
| Shared IP address with a bad reputation | You send from an IP address used by other customers, and one of them is spamming. Your emails pay the price. Here is how to tell and what to ask your provider. | Fix it | |
| A hacked email account is sending spam: what to do | Someone has your password and is sending spam from your mailbox. Lock them out, remove what they left behind, then repair your reputation. | Fix it | |
| Choose a good sender name and From address | The sender name and address are the first things people see. Pick ones that are clear, stable and on your own domain, and readers trust and open your emails. | Fix it | |
| Why "no-reply" addresses hurt your emails | Sending from noreply@ tells readers you do not want to hear from them. It costs you replies, trust and sometimes inbox placement. Use a real address instead. | Fix it | |
| Inactive subscribers hurt your reputation: re-engage or remove them | People who never open your emails drag down your reputation and can hide spam traps. Try to win them back once, then stop emailing those who stay silent. | 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 | |
| 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 | |
| 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 | |
| Set up Google Postmaster Tools step by step | Google Postmaster Tools is Gmail's free dashboard for senders. Verify your domain once and watch your spam rate and compliance status. | Fix it | |
| Use a custom tracking domain for links in your emails | Newsletter tools rewrite your links through a shared tracking domain. If that domain gets a bad name, your emails suffer. Use your own instead. | Fix it | |
| Gmail "550-5.7.1 ... likely unsolicited mail": why it happens and how to fix it | Gmail rejected your email as likely spam. Learn what triggers 550-5.7.1 unsolicited mail and how to fix authentication, reputation and content. | Fix it | |
| Gmail "421-4.7.0 ... very low reputation of the sending IP address": how to fix it | Gmail is temporarily deferring your emails because of low IP or domain reputation. Learn why 421-4.7.0 happens and how to rebuild your reputation. | Fix it | |
| Gmail "550-5.7.28 ... unusual rate of unsolicited mail from your IP address": how to fix it | Gmail blocked your IP after detecting an unusual rate of unsolicited mail. Find the source of the spam, stop it and rebuild your reputation. | Fix it | |
| Outlook.com "550 5.7.1 ... part of their network is on our block list (S3150)": how to fix S3150 and S3140 | Outlook.com and Hotmail refuse your email because your IP or its network range is on their block list (S3150, S3140). Learn how to request delisting. | Fix it | |
| Yahoo "421 4.7.0 [TSS09] All messages from [IP] will be permanently deferred; Retrying will NOT succeed": what to do | Yahoo has stopped accepting mail from your IP because of poor reputation. Why TSS09 happens, how to recover and how to contact Yahoo. | Fix it | |
| iCloud "554 5.7.1 [CS01] Message rejected due to local policy" and "[HM08]": how to fix it | Apple iCloud Mail refused your email with CS01 or HM08. What these codes usually mean and how to fix authentication and reputation. | 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 | |
| "554 5.7.1 Service unavailable; Client host [IP] blocked using zen.spamhaus.org": what it means and how to fix it | The receiving server found your IP on Spamhaus ZEN (SBL, XBL or PBL). How to find which list, fix the cause and get removed. SpamCop too. | Fix it | |
| Mimecast "550 Rejected by header based Anti-Spoofing policy", "Envelope blocked" and Proofpoint "554 5.7.0 Blocked": fixes | Company email filters like Mimecast and Proofpoint blocked your email. What their bounces mean, what you can fix and how to ask the recipient's IT team. | Fix it |
Not sure what is wrong?
Send a test email or scan your domain: the report tells you which problem you have.