// 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
13 guides · tag Gmail
| Problem | In short | Tags | |
|---|---|---|---|
| Gmail and Yahoo bulk sender requirements | Since 2024, Gmail and Yahoo require large senders to authenticate their emails, offer one-click unsubscribe and keep spam complaints very low. Here is the checklist. | Fix it | |
| 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 | |
| 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 | |
| Add a List-Unsubscribe header (one-click unsubscribe) | The List-Unsubscribe header lets Gmail, Yahoo and Outlook show an Unsubscribe button next to your sender name. Bulk senders must offer it in one click. | 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 | |
| Missing or wrong Date and Message-ID headers | Every email should carry a correct Date and a unique Message-ID. Without them, spam filters add points and Gmail can refuse the email. | Fix it | |
| Gmail shows "via" or "sent on behalf of" next to your name | Recipients see "via another-domain.com" or "on behalf of" because your email is signed or sent with another domain. Sign it with your own domain. | Fix it | |
| Your emails land in Gmail's Promotions tab | The Promotions tab is not spam: Gmail is sorting your marketing emails. Learn when it is normal, and what helps personal and transactional emails stay in Primary. | Fix it | |
| Email too big: Gmail clips messages over 102 KB | When the HTML of an email is larger than about 102 KB, Gmail cuts it and shows "[Message clipped]". Your unsubscribe link and footer can disappear. | Fix it | |
| Gmail warning "Be careful with this message" | Gmail shows a yellow or red banner on your email because it could not confirm you sent it. Fix your authentication and the warning goes away. | 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 | |
| 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 | |
| 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 |
Not sure what is wrong?
Send a test email or scan your domain: the report tells you which problem you have.