Home Blog How To Prevent Winmail. dat Email Attachments in Office 365

How To Prevent Winmail. dat Email Attachments in Office 365

 2021/01/16   Microsoft Cloud Solutions   1433 visit(s)


 Musab Ghannaj


Just a while ago, I was working on a project migrating users from Lotus Domino IBM email system to Office 365. At that point, I encountered a strange issue after moving a certain number of users to Office 365. It went like this: Emails passing from migrated users to unmigrated ones were received in Plain Text Formatting instead of Rich Text Formatting. This means all emails delivered from migrated users to their fellow yet-to-be-migrated ones (including HTML signatures, tables of rows or columns…etc.,) looked terrible and messy on the receiver’s side.

Here's how you can solve this issue...

By default, email messages that are sent from Exchange Online in Office 365 use the Transport Neutral Encapsulation or (TNEF) format. Messaging systems that aren't based on Microsoft Exchange - like Lotus Domino in my case - were seemingly unable to interpret messages that use this rich text format even when they belong to the same domain.

To solve this issue, there are two options: PowerShell Commands or Office 365 ECP portal. In this blog, I will focus on employing PowerShell to help get things sorted.

Using PowerShell:

1. Connect to Exchange as a global admin.

  • Note: Here you will find how to connect to Exchange Online using PowerShell

2. Create a new Remote Domain using the below code:

New-RemoteDomain -Name Contoso -DomainName Contoso.com

  • Note: Replace Contoso with your domain name and contoso.com with your domain.com

Set-RemoteDomain -Identity Contoso -TNEFEnabled $false

Get-RemoteDomain -Identity Contoso | Select TNEFEnabled

Wait for at least an hour and test the email again.

Hope this is going to solve the prroblem for you.

Note: Here you will find how to connect to Exchange Online using PowerShell.

Musab Ghannaj,

Ctelecoms Team

Search the Blog

Subscribe Blog



IT & Cyber-Security Solutions

Best-in-class cyber security solutions to ...


Microsoft Cloud Solutions

Explore Ctelecoms extensive selection of ...


Datacenter Solutions

Solve issues, streamline operations, promote ...


Cloud Backup & Disaster Recovery Solutions

Keep your data, apps, emails and operations ...


Computing & Hyper-converged Infrastructure Solutions

Take your IT infrastructure to the next level ...


Unified Communications & Networking Solutions

Ensure you are securely connected with all ...


Meraki Networking Solutions

Quickly deploy a reliable, secure, cloud-managed ...