Fix: Sender Verification Failed

What's Happening

You're trying to send an email, but it bounces back with an error like "Sender Verify Failed" or "Domain of sender address does not exist." The recipient's email server is rejecting your message because it can't verify that your sending domain is legitimate.

Why This Happens

When you send an email, some receiving servers perform a check to confirm your domain exists and is properly configured. They do this by looking up your domain's MX (Mail Exchange) records in DNS. If those records are missing or misconfigured, the server assumes your domain isn't real and blocks your message.

This happens most often when you're using a custom sending domain or subdomain (like send.yourdomain.com) that doesn't have MX records set up. Some email providers—especially corporate and government servers—are strict about this. Others ignore it entirely.

Common Error Messages

You might see any of these variations:

• 550 Verification failed for you@yourdomain.com
• Domain of sender address does not exist
• Sender address rejected: User unknown in virtual mailbox table
• 450 4.1.8 Sender address rejected: Domain not found
• 452 4.5.2 Could not resolve sender domain
• 550 5.2.0 From: Domain is invalid
• 550 5.7.1 Sender ID (PRA) Domain Does Not Exist

They all point to the same problem: missing or incorrect DNS configuration.

How to Fix It

1. Add MX Records for Your Sending Domain

Even if you're not receiving incoming mail at your sending domain, you need to set up MX records so recipient servers can verify it exists.

Log in to your domain registrar or DNS provider (wherever you manage your domain settings) and add these two MX records for your sending subdomain:

For example, if your sending domain in the system is send.yourdomain.com, replace "subdomain" with "send" in the hostname field.

This tells email servers that your domain is real and properly configured, even if you're not actually receiving mail there.

2. Wait for DNS Propagation

DNS changes take time to spread across the internet. Allow 24–48 hours for the updates to propagate globally. During this window, some emails may still fail with the same error.

3. Test Your Setup

After 24–48 hours, send a test email to the recipient who was getting the error. If it goes through, your fix worked. You can also use a DNS checking tool like mxtoolbox.com to verify your MX records are now visible.

4. Still Having Issues?

If the error persists after DNS propagation, contact support. We can verify your domain configuration and help troubleshoot any remaining issues.

Questions and Answers

Q: What is an MX record and why does it matter?

A: MX records are DNS settings that tell email servers where to deliver incoming email. Some receiving servers also use them to verify that your domain exists before accepting outgoing messages from you. Without MX records, those servers assume your domain is fake and block your email.

Q: I'm using a custom domain like send.mycompany.com. Do I still need MX records if I don't receive mail there?

A: Yes. Even if you're not receiving mail at that subdomain, some recipient servers check for MX records before accepting your outgoing email. Adding them proactively prevents this error from happening.

Q: How do I know if my DNS changes are working?

A: Use a tool like mxtoolbox.com to check your DNS records. Enter your sending domain (like send.yourdomain.com) and look for the MX records you added. Once they appear in the results, your changes have propagated.

Q: Does this issue affect every email provider?

A: No. Some email providers ignore missing MX records and accept your mail anyway. Others—especially corporate, government, and education servers—are stricter and will reject your message outright. It's impossible to predict which ones will block you, so it's best to set up MX records.

Q: Can I just use a free Gmail, Yahoo, or Outlook address instead?

A: You can, but we don't recommend it. Custom domains look more professional and give you better deliverability when properly configured. Free email addresses also come with sending limits and can trigger spam filters more easily.

Q: What if I need help updating my DNS settings?

A: Most domain registrars have documentation or live support to walk you through DNS changes. If you're not sure how to do it, you can also click "Send DNS Details to Your Tech Team" from within the system, and we'll email them the exact settings they need to add.

Q: Is this related to DMARC, SPF, or DKIM setup?

A: Not directly, but those authentication tools are also important for email deliverability. MX records verify your domain exists. SPF, DKIM, and DMARC verify you're authorized to send from that domain and protect against spoofing. They work together to improve your sender reputation.

Guide Type: Fixes & Troubleshooting

Estimated Time: 30 minutes (including DNS propagation wait time)

Next Guides: Setup: Email Sending Domain, About: Email Authentication, How to Test Email Deliverability