Troubleshooting the "Sender Verify Failed" Email Error

Overview

If you're seeing an error like "Sender Verify Failed" when sending emails, this guide will help you understand what it means and how to fix it.

What the Error Means

This error (also known as Sender Address Verification) typically occurs when the receiving server performs an MX (Mail Exchange) lookup on your sending domain and can't find valid DNS or MX records. If those records don’t exist or are misconfigured, the recipient’s email server rejects your message.

Here are a few common variations of this error message:

• 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

Why It Happens

Some email providers are stricter than others and may block your message if they can’t confirm that the domain in your “From” email address exists and is properly configured. If you're using a subdomain (like send.yourdomain.com), it’s especially important to ensure the DNS settings are correctly configured.

How to Fix It

1. Set Up MX Records for Your Subdomain

Even if you're not receiving incoming mail at this subdomain, setting up Mail Exchange (MX) records can resolve this issue.

For example, if your sending domain in AllClients is send.yourdomain.com, you should add these two MX records for that subdomain in your DNS provider’s settings:

Tip: You only need to do this if you’re using a custom sending domain in AllClients.

2. Wait for DNS Propagation

After updating your DNS records, it may take up to 24–48 hours for the changes to propagate globally. During this time, some emails may still fail to send.

3. Test Your Setup

Once your DNS records have propagated, test sending an email again. If the error goes away, your fix worked!

4. Still Not Working? Contact Support

If you’ve followed these steps and still see the error, our support team can help verify your domain configuration and troubleshoot further.

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 use them to verify that your domain exists before accepting your message.

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

A: Yes. Even if you’re not receiving mail at that subdomain, some recipient servers check for MX records anyway. Adding them proactively prevents this issue.

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

A: Use a tool like mxtoolbox.com to check your DNS records. Once your MX records are listed, you should be good to go.

Q: Does this issue affect every email provider?

A: No. Some email providers ignore missing MX records, but others (like some corporate or government servers) are stricter and will block your message.

Q: Can I 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. Learn why here »

Q: What if I need help updating DNS settings?

A: Most domain registrars have documentation or live support to help you make these changes. If you’re not sure, you can also click “Send DNS Details to Your Tech Team” from within AllClients, and we’ll send them the right info.

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

A: Not directly, but those are also important email authentication tools. They work together to improve deliverability and reduce the risk of email spoofing.