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Why am I receiving defer notification for reason of Recipient Verification Unavailable on my Email Security Gateway?

  • Type: Knowledgebase
  • Date changed: 2 years ago
Solution #00003765

All Email Security Gateways, All Firmware Versions.

Please check to make sure you are not using a "catch-all" domain such as an asterisk ( * ). This causes the Barracuda recipient verification process to become unavailable for a short period of time. The verification process relies on an actual domain name to perform its job properly. Please change this to your actual domain name.

Another issue that you may be running into is the LDAP filter you are using.

Best practice for the LDAP filter is to keep it as short and correct as possible

PLEASE check the LDAP Filter when you see LDAP timeout or Recipient Verification Unavailable errors.

If your filter is long and complex then it may be causing errors which can crash the recipient verification service on the Barracuda unit. For example this is one of our default filters

( (othermailbox=smtp$${recipient_email})(othermailbox=smtp:${recipient_email})(proxyaddresses=smtp$${recipient_email})(proxyaddresses=smtp:${recipient_email})(mail=${recipient_email})(userPrincipalName=${recipient_email}))

In most cases all that is actually required is this (for MS Exchange)

( (mail=${recipient_email}))

or this (if they use aliases/proxy addresses)

( (proxyaddresses=smtp:${recipient_email})(mail=${recipient_email}))

In the Barracuda the longer and more complex the LDAP filter the longer the query takes to run and if there are invalid attributes or requests in the query it can cause the recipient verification services to crash.

Keep the LDAP filter as short and accurate as possible.

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