cPanel / WHM Server Email Sending Error (SMTP Error 550) Solution

Why Aren't Your Emails Reaching the Other Side?

The "550 Please turn on SMTP Authentication" or "550 High probability of spam" errors you get when sending mail from sites or corporate email addresses hosted on your own virtual server infrastructure indicate that your email traffic is blocked. There are several main technical reasons for this problem on cPanel / WHM.

1. Lack of SMTP Authentication

If your mail client (Outlook, Thunderbird, or your phone's mail app) connects to the server by only entering a password and not checking SMTP authentication, cPanel rejects the mail to prevent spam sending. In Outlook, if you go to your email account properties and check the "My outgoing server (SMTP) requires authentication" option, the 550 error will be fixed instantly.

2. IP Address Blacklist Check

The reason why emails going out of your server go straight to the trash box (Spam) or are rejected by Gmail/Hotmail servers with a 550 error code is that the IP address of your VDS server has entered global blacklists (Spamhaus, CBL, etc.). Query your IP address via MxToolbox. If you are on a blacklist, first change your passwords and scan for viruses, then create a delist request.

3. Missing DNS (SPF, DKIM, DMARC) Records

Go to the "Email Deliverability" menu in cPanel and check your site's DNS records. Today, emails from servers missing SPF (Sender Policy Framework), DKIM, and DMARC records are rejected directly. By pressing the "Repair" button in this menu, you can have cPanel automatically create these DNS records for you.

If you want to achieve a 100% delivery rate in mail services and use a professional infrastructure with clean IP addresses, you can meet our corporate İyibirNet VDS Server services!