If you're encountering a "550 email rejected by recipients" error—commonly referred to as a 550 SMTP error—when trying to send an email, this guide will help you troubleshoot the issue.
In short, this error means your email was rejected and not delivered because the recipient’s server did not accept it. This is a permanent failure, meaning the message won’t be retried.
Common causes of SMTP 550 errors
There are several possible reasons why this error occurs. Below we list some of the most common causes and steps you can take to resolve them.
1. Invalid recipient email address
This is the most common and simplest cause. The email address you’re sending to either doesn’t exist or was mistyped. The error may read “550 5.1.1 User unknown,”“550 5.1.0 Address rejected,” or something similar.
Consider the following steps:
Double-check the recipient’s address for typos.
Contact the recipient by other means to confirm their email address.
2. Recipient mailbox full
If the recipient's inbox has reached its storage limit, incoming emails may be rejected until space is freed up. The error may display a message like "550 5.2.2 Mailbox full".
Try the following:
Contact the recipient another way to inform them of the issue.
Wait a few hours days and then retry.
3. Your domain/IP is blacklisted
Your sending IP address or domain may be blacklisted due to past spam complaints, high bounce rates, or suspicious activity, which can cause the recipient's server to block your emails.
You'll typically see a more descriptive message like:
"550 5.7.1 Service unavailable; Client host [xxx.xxx.xxx.xxx] blocked using <blacklist>"
What you can do:
Check your IP/domain reputation using MXToolbox Blacklist Check.
If you find a listing, follow the removal instructions provided by that blacklist.
Send the email using another email address or network.
4. Suspicious content or attachments
The content of your email may trigger the recipient's spam filters or violate their server's policies. You might see an error such as: "550 5.7.1 Message rejected due to content policy" or something similar.
To resolve the issue:
Avoid using spammy language or suspicious-looking links.
Refrain from attaching files in formats commonly associated with malware or phishing.
Send a plain-text email with no attachments or links to see if it goes through.
Reduce the number of recipients per message (e.g., limit to 10–20 recipients at a time).
Ask the recipient to add your email address or domain to their whitelist.
5. Missing or invalid email authentication (SPF, DKIM, DMARC)
If your sending server is not properly authenticated using SPF, DKIM, or DMARC, the recipient’s server may reject your message, flagging it as potentially fraudulent or spoofed.
This can result in errors like "550 5.7.1 SPF check failed” or “550 5.7.1 Message not accepted due to failed DMARC policy”.
Steps to take:
Add SPF, DKIM, and DMARC records to your domain's DNS settings.
Use tools like MXToolbox, DMARC Analyzer, or dmarcian to check your DNS records and get setup guidance.
If your email domain is registered with GoHosting and uses its DNS, you can add or edit SPF and DMARC records directly in cPanel.
Ensure your SPF record includes all email providers you use, such as Google Workspace or Microsoft 365.
6. Too many messages sent in a short time
Some email hosting providers place limits on how many emails you can send within a 24-hour period. Likewise, some recipient servers may throttle or block your messages if too many are sent, as a precaution against spam.
You might receive an error like: "550 5.2.1 Rate limit exceeded,""550 5.4.5 Daily sending quota exceeded," or similar.
Consider the following:
Reduce the number of emails you send in a 24-hour window.
Use a dedicated email marketing service, such as Mailchimp, for bulk sends.
7. Message size exceeds maximum limit
Email servers often have strict size limitations for incoming messages, typically ranging from 10MB to 25MB.
If your message exceeds this limit, you might see an error like: "550 5.7.1 Message size exceeds fixed maximum message size".
To fix this:
Compress files or reduce image sizes to make attachments smaller.
Upload large files to a cloud file-sharing service and share the link.
Split the content into multiple emails if needed.
