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Inbound Email Attachments Saved as 'winmail.dat' in Salesforce Email-to-Case (Microsoft Outlook Rich Text Format Issue)

Julkaisupäivä: May 1, 2026
Kuvaus

When Salesforce receives an inbound email via Email-to-Case, the attachment appears as a file named winmail.dat instead of the original file the sender attached.
The winmail.dat attachment behavior is a known issue with Microsoft Outlook when it uses an Exchange Server to send emails. This issue originates outside of Salesforce — it is not caused by the Salesforce inbound messaging system.
A winmail.dat file is generated when:

  • The email is sent from Microsoft Outlook.
  • The email format is set to Rich Text Format (RTF). RTF is a proprietary Microsoft email formatting standard that encodes message formatting and attachments into a Transport Neutral Encapsulation Format (TNEF) file, which appears as winmail.dat to non-Outlook recipients.

Root Cause

Microsoft Outlook automatically converts email attachments into a winmail.dat TNEF file when the outgoing email format is set to Rich Text Format (RTF). Email clients that are not Microsoft Outlook — including the Salesforce inbound email processor — cannot decode TNEF files, so the attachment arrives as winmail.dat instead of the original file.
This is a sender-side configuration issue in Microsoft Outlook or Exchange Server, not a Salesforce bug.

Ratkaisu

To prevent inbound attachments from arriving as winmail.dat in Salesforce Email-to-Case, the sender's Microsoft Outlook configuration needs to be updated to use HTML or Plain Text email format instead of Rich Text Format (RTF).
Option 1 — Change the default format for a specific contact in Outlook:

  1. In Microsoft Outlook, open the Contacts folder.
  2. Open the contact record for the affected sender.
  3. Double-click the email address field.
  4. In the Email Properties dialog, change the Internet format dropdown from "Send using Outlook Rich Text Format" to "Send as Plain Text" or "Send as HTML".
  5. Click OK and save the contact.

Option 2 — Change the global default email format in Outlook:

  1. In Microsoft Outlook, go to File | Options | Mail.
  2. Under the Compose messages section, change Compose messages in this format to "HTML" or "Plain Text".
  3. Click OK.

Option 3 — Exchange Server-level fix (for administrators):
An Exchange Server administrator can configure the server to convert RTF to HTML for outbound SMTP messages, preventing TNEF encoding entirely.
After the sender updates their format, future emails from that sender arrive in Salesforce Email-to-Case with properly attached files.
Note: This change must be made by the email sender or their IT/Exchange administrator. Salesforce administrators cannot resolve this issue from within Salesforce.

Knowledge-artikkelin numero

000385576

 
Ladataan
Salesforce Help | Article