Priority: 1


Affected Service:

Customers using us1-smtp-ui.titanhq.com on the SpamTitan Cluster, 

this started on July 24th, around 6AM GMT / 2PM ET US

Summary

Office 365 tenants are currently deferring messages with the SMTP response "451 4.7.500 Server busy." This affects customers utilizing the us1-smtp-ui.titanhq.com.

Solution

To resolve this issue, we recommend creating a "Partner Organization to Office365 Connector". This will help prevent message deferrals and ensure your emails are accepted immediately.

Please follow the instructions provided in this guide.


SpamTitan IP Addresses:

  • 18.218.73.72
  • 18.116.252.179
  • 18.225.12.231
  • 3.20.181.16
  • 3.21.255.101

Impact

To resolve this issue, we recommend creating a "Partner Organization to Office365 Connector". This will configure your Office365 Tenant to treat SpamTitan like a "partner", and not throttle message delivery w/"451 4.7.500 Server busy" message deferrals and ensure your emails are accepted immediately.

We appreciate your attention to this matter and apologize for any inconvenience caused. Thank you for your cooperation.


Update:
24 July, 4:15 PM ET -- We are Still seeing a lot of "451 4.7.500 Server busy" when attempting to relay to Office365.   The Partner Organization connector if the best way around this is you are using Office365 and your mail is getting delayed. 

25 July, 8:45 AM ET 
Also, since it is the Office365 tenants that are responding with "451 4.7.500 Server busy", you may want to reach out to Office365 Support and mention:  

'We are using a 3rd party mail filter (SpamTitan) and Office365 is saying ""451 4.7.500 Server busy", and it's impacting our business."

25 July 3:30 PM ET
The number of "451 4.7.500 Server busy" fro Office365 has dropped significantly, especially for domains that have created Partner Connectors.