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Sender Verification Error

The Sender Verification Error (or Sender Address Verification) occurs when the recipient server performs a MX lookup on the envelope.mail-from address and it fails to locate the MX records for the sending domain. The error can appear in a few different ways - Here are the most common:

  •  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
  • Server response: 550 550 Verification failed for <bounce+c72392.3559d@yoursendingdomain.com> Unrouteable address Sender verify failed

 We'll explore several ways to resolve this error based on your current Mailgun sending domain! 

Subdomain

When configuring any subdomain with Mailgun, we don't require MX records to be used, but we do highly advocate that they are to proactively correct this issue before it begins! As noted above, some pesky email servers check the subdomain in the envelope.mail-from field for MX records and if those records aren't found, then BAM! You'll get hit with a Sender Verification Error in your Mailgun logs. Not to worry though - the fix is easy!

The fix is to simply add Mailgun's MX records to your subdomain! 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:

Value Priority
mxa.mailgun.org 10
mxb.mailgun.org 10

Once the records have been added, you'll need to wait the 24-48 hours for them to fully propagate and the error should disappear!

One final tip - If you're still seeing it, please also try adjusting the From field of the message to match the sending domain as well.

Root Domain

On to the root domain approach! In this instance, 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 will be resolved!

Alternate Approaches

These are the final options for resolving the error - It's highly recommended to review and implement the above suggestions before moving on to these! They are:

  1. Turn off sender address verification (this is server-side)
  2. Add "x-mailgun-native-send: true" to the header of your message to turn off sender address rewriting
  3. Create a catch_all with the service where you receive email so that, when the recipient server checks, verification it will pass

 

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