For some time (more than a week) every 6 hours in the event log these errors occur:

Event: '3025'
Category: 'Extension'
Source: 'MSExchangeApplicationLogic'
Message: 'Failed to download killbit list from OMEX server. Exception: System.Net.WebException: Serwer zdalny zwrci bd: (404) Not Found. w System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult) w Microsoft.Exchange.Data.ApplicationLogic.Extension.BaseAsyncOmexCommand.<>c__DisplayClass2.<EndGetResponseCallback>b__1()'

and:

Event: '3018'
Category: 'Extension'
Source: 'MSExchangeApplicationLogic'
Message: 'The request failed. Mailbox: Url: https://office.microsoft.com/client/15/appinfo/query?rt=XML Exception: System.Net.WebException: Serwer zdalny zwrci bd: (404) Not Found. w System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult) w Microsoft.Exchange.Data.ApplicationLogic.Extension.BaseAsyncOmexCommand.<>c__DisplayClass2.<EndGetResponseCallback>b__1()'

Has anybody else also noticed it and know what's going on?

Hi przemyslawb,

Thank you for your question.

Could you provide us more details for our troubleshooting.

For example: Whats the Exchanges version? Are there any effects on organization...

We have two options here regarding the errors:

Option 1 : Since there will be no user who will download the app, safely ignore the errors logged.

Option 2: If possible add https://o15.officeredir.microsoft.com/* URL in the proxy server as exception.

If there are any questions regarding this issue, please be free to let me know. 

Best Regard,

Jim