Office 365 mailbox (Exchange online) with winmail.dat attachments


Receiving emails in office 365 mailbox (Exchange online) with winmail.dat attachments


Issue Description:  Customer is receiving emails with winmail.dat attachments.

Cause: This is due to Office365 setting the default attachment format to TNEF. This format causes issues with mail clients that are unable to read this attachment format, thus creating the WINMAIL.DAT issue.

Resolution:  The solution is disabling the TNEF via Office365 Portal as:

  1. In Exchange Admin Centre, Go to Mailflow>>Remote Domains.
  2. Select Use Rich-text Format as Never.
  3. Save it.

One can also use PowerShell to turn the conversion off as:

  1. $Cred = Get-Credential
  2. Type in your Office365 admin user credentials
  3. Connect-msolservice -credential $Cred
  4. $Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/ -Credential $Cred -Authentication Basic -AllowRedirection
  5. Import-PSSession $Session
  6. Set-RemoteDomain Default -TNEFEnabled $false
  7. Remove-PSSession $Session

Referenced Link:
Manage TNEF Message Formatting with Remote Domains: https://msdn.microsoft.com/en-us/library/gg263346(v=exchsrvcs.149).aspx


Comments

  1. Christina Bedford8 January 2021 at 17:17

    The good news is, if you don't need the full suite of Microsoft 365 tools, you can access a number of its apps online for free -- including Word, Excel, PowerPoint, OneDrive, Outlook, Calendar and Skype. Here's how to get them: Go to Office.com. Login to your Microsoft account (or create one for free).
    for more information click here: how to add another email account to outlook 2016

    ReplyDelete

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