Overview

This error (also called Sender Address Verification) occurs when the recipient server performs an MX lookup on the envelope.mail-from address and then fails to locate the MX records for the sending domain.  (See this wiki for a deeper dive into the technical details of Sender Address Verification)

You might see this manifest in a few different ways; here are a few of the most common variations:

• 550 Verification failed for <bounce+c72392.3559d@yoursendingdomain.com>\nUnrouteable address\nSender verify failed
• Domain of sender address bounce+c72392.3559d@yoursendingdomain.com does not exist
• 550 550 Verification failed for <bounce+c72392.3559d@yoursendingdomain.com>
• Unrouteable address Sender verify failed
• Sender address rejected: User unknown in virtual mailbox table
• 452 4.5.2 Could not resolve sender domain
• 450 4.1.8 Sender address rejected: Domain not found
• 505 Your domain has no DNS/MX entries
• 550 550 Requested action not taken: mailbox unavailable invalid DNS MX or A/AAAA resource record
• 550 5.2.0 <bounce+c1b91d.4ce06-example=domain.tld@mg.domain.tld> From: Domain is invalid. Please provide a valid From: IB506 <http://x.co/srbounce>
• 550 550 5.7.1 Sender ID (PRA) Domain Does Not Exist

Now that we've seen the errors, we'll explore several ways to resolve this issue based on your current Mailgun sending domain.

Seeing this issue with a subdomain

When configuring any subdomain with Mailgun, while we don't require MX records to be used, as long as you don't already have incoming mail configured for the domain, we highly recommend pointing your MX records for the domain to Mailgun. Why? Doing so serves to proactively correct the Sender Verification Error issue before it begins - always good to be ahead of the curve!

As noted above, some pesky email servers check the subdomain in the envelope.mail-from field for MX records. If those records aren't found, then you're hit with a Sender Verification Error in your Mailgun logs. All is not lost, however - the fix is quite simple; just set the MX records for the subdomain to Mailgun values!

Once this is completed, the MX lookups of those email servers should be successful and the servers should accept your messages.

The two MX records for Mailgun that will need to be added to your subdomain are:

Once the records have been added, you may need to wait the 24-48 hours for them to fully propagate; following this, the error should disappear.

If for any reason you're still seeing that same error, you will need to complete this change by adjusting domain in the From field of the message to match the sending domain as well.

Seeing this issue with a root domain

What if you're using a root domain*? In this case, your root domain already has your ESP's (Email Service Provider) MX records in place. The best and safest way to quickly resolve this would be to add a subdomain for your Mailgun sending instead.  

When the subdomain is added, along with Mailgun's MX records configured for it, the error should be resolved!

(* Caveat: If your root domain does not have and will not need any MX records pointing to a hosted mailbox provider, you can add the root domain to your Mailgun account, verify the required TXT AND MX records, and send through the root domain)

NOTE: Always make sure your MX records for a domain only point to one source. If you were to configure Mailgun's MX records on your domain, and your domain already has MX records pointing to your email hosting provider, all inbound emails could be redirected to Mailgun and away from your hosted mailboxes (or worst: dropped or lost altogether!). 

Alternate approaches

Still having issues? While fairly uncommon after performing the steps above, it is possible you will still see the error, especially if you're using Mailgun to send from your domain and it is arriving to your domain (i.e. your provider does not like seeing email from your domain coming from an outside system).  Not to worry!  There are alternate options for resolving the error. Please make sure to note - it's highly recommended to review and implement the above suggestions before moving on to these:

1. Turn off sender address verification (this is server-side with your email provider)
2. Create a catch all within the configuration of your email provider so that when the recipient server checks the sender information for the incoming emails, Sender Address Verification will pass

Need Support?

Our Support Team here at Sinch Mailgun is happy to help! Reach out to us in the Support page of your Mailgun Control Panel, and we'll be with you shortly!