Error Message

No error message is displayed. 

If an email is sent using Rich Text Format (RTF) while TNEF is enabled, the EML message will have an attached file called winmail.dat.

The Content-Type in the header information of the EML message will show as follows:
Content-Type: application/ms-tnef; name="winmail.dat"
 

Determine if TNEFEnabled is set to true in the Exchange environment.

1. From Exchange Management Shell run the following command:

Get-RemoteDomain | Select Name, DomianName, TNEFEnabled

2. If TNEFEnabled = True for the Remote Domain then set it as disabled as follows:

Set-RemoteDomain -Identity -TNEFEnabled $false

Microsoft documentation: 
How to specify the email message format that's used for external recipients to prevent Winmail.dat attachments

The journal contact should be set to -UseMapiRichTextFormat Never per the EV.cloud configuration guide.