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Customer experience | Sales, Customer Insights,...
Answered

Dynamics Sales Emails Going Out in Old Winmail Format, Not HTML

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Posted on by 16
We have an issue where emails we are sending from inside Sales Hub with email templates are using the older Microsoft Transport Neutral Encapsulation Format (TNEF).
 
In non-MS mail clients, like Gmail, instead of showing the HTML, it shows the plain text version and a winmail.dat file attachment.
 
This looks bad to recipients, and the attachment can cause concern.
 
Is anyone else seeing this problem? Do you know how we can address it?
 
Using Outlook is not an option, as we are doing Sequences.
 
We have also checked Exchange and have no defaults that enable TNEF.
 
Thank you in advance.
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  • Suggested answer
    ManoVerse Profile Picture
    1,281 Super User 2026 Season 1 on at
    issue is typically caused by emails being sent in TNEF (winmail.dat) format, which is not supported by non-Microsoft clients like Gmail. Even if Exchange defaults are correct at your end, this can still occur due to:
    Email templates using rich text formatting which use TNEF , Server-side sync behavior in Sequences and  Remote domain or mailbox-level TNEF settings can cause this. 
    fix you can follow like below , reference link also there :
    1) ensure templates use HTML (not rich text)
    2) disable TNEF in Exchange (Set-RemoteDomain -TNEFEnabled $false) Command like below :
    Set-RemoteDomain Default -TNEFEnabled $false
    3)Avoid RTF in Dynamics email , in Email editor uses HTML format , No embedded RTF content
    Rebuild problematic templates from scratch if needed
     
    This should resolve your issue.
  • Suggested answer
    11manish Profile Picture
    962 on at
    Based on your setup:
     Email templates or Sales Hub email generation is introducing RTF formatting that triggers TNEF encoding during server-side sync.
     
    Recommended fix path 
    • Rebuild email templates (clean HTML only)
    • Test sequence email vs manual email
    • Verify email record BodyType = HTML
    • If still failing → enforce Exchange remote domain rule for Gmail
    • Validate email headers
  • Verified answer
    CU07012210-0 Profile Picture
    16 on at
    I was able to dig deep and figure out the problem. It is an issue between Azure AD and Exchange, not Dynamics Sales.

    The receipt test email address on Gmail was an Azure AD Guest User.

    This caused Azure AD created a MailUser object to represent that guest. Exchange Online treats MailUsers as internal recipients, and they can have RTF/TNEF formatting enabled, even if the domain is external. Why it chose RTF/TNEF is a mystery.

    Since this issue only affects those users, we won't be resolving it.

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