When users try to access their Exchange Online mailbox in Microsoft Outlook or Outlook on the web (formerly known as Outlook Web App), event ID 1014 is logged multiple times in the System log in Event Viewer:
Log Name: System Source: Microsoft-Windows-DNS-Client Date: <Date> <Time> Event ID: 1014 Task Category: (1014) Level: Warning Keywords: (268435456) User: NETWORK SERVICE Computer: <ComputerName>.contoso.com Description: Name resolution for the name outlook.office365.com timed out after none of the configured DNS servers responded.
This issue may occur if the request was blocked by third-party malware or an Internet protection suite. The time to live (TTL) on the outlook.office365.com DNS record is five minutes. Therefore, Windows refreshes the record at an interval of five minutes. Third-party malware and Internet protection suites have been found to block the request at this frequency, which prevents users from using Outlook or Outlook on the web to connect to their Exchange Online mailbox.
Work with your third-party vendor to set up exclusions for the outlook.office365.com DNS record.